It is the sentimentality of our past, usually for a particular time and place associated with positive emotions, etched in our memories. Historical texts state it was termed as homesickness during war times.It is now considered a natural, common emotion, a way to escape from the current 'space-time' and mentally travel to one's past when the world around us was different. It is usually prompted by a feeling of loneliness, disconnectedness or meaninglessness, triggered by thoughts about the past, by our senses of smell and touch or through music or weather.

Nostalgia

Self Improvement

The feeling of nostalgia is like traveling in a time machine. The activities that were once cherished are no longer done, and the world that is remembered no longer exists.
Nostalgia can be a form of self-deception, giving a rosy tint to the past, creating a paradise out of the moments of our lived lives.
Deep nostalgia fosters a sense of serene melancholy and spiritual longing.

A Time Machine

The deepest form of suffering is a feeling of extreme dissatisfaction about the impermanence and the insubstantiality of everything around us.
Buddhism mentions suffering as inevitable as long as there is desire, lust and a sense of coveting/craving in our lives. Once we grasp this fully, we stop craving and struggling in hope and fear.

Suffering

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<img src="https://cdn.psychologytoday.com/sites/default/files/styles/image-article_inline_full/public/blogs/89816/2014/11/165557-170224.jpg?itok=rLs7ecdA">Nostalgia is sentimentality for the past, typically for a particular period or place with positive associations, but sometimes also for the past in general, 'the good old days' of yore. At the end of Andr&#233; Brink's novel, An Instant in the Wind, the character of Adam memorably says, 'The land which happened inside us no one can take away from us again, not even ourselves.' Nostalgia combines the sadness of loss with the joy or satisfaction that the loss is not complete, nor can ever be. Mortal though we are, whatever little life we have snared from the legions of death is forever ours.
'Nostalgia' is a portmanteau neologism coined in 1688 by Swiss medical student Johannes Hofer from the Greek n&#243;stos (homecoming) and &#225;lgos (pain, ache). N&#243;stos is, of course, the overriding theme of Homer's Odyssey, in which Odysseus strives to return to Penelope and Telemachus and his native Ithaca in the aftermath of the Trojan War. In Virgil's Aeneid, Aeneas, another survivor of the Trojan War and the ancestor of Romulus and Remus, gazes upon a Carthaginian mural depicting battles of the Trojan War and the deaths of his kin. Moved to tears, he cries out, sunt lacrimae rerum et mentem mortalia tangunt: 'These are the tears of things and mortal things touch the mind.' 
Hofer coined 'nostalgia' to refer to the homesickness of Swiss mercenaries fighting in foreign lowlands. Military physicians attributed this homesickness, also known as Schweizerheimweh or mal du suisse, to ear and brain damage from the constant clanging of cowbells. Recognized symptoms included pining for Alpine landscapes, fainting, fever, and even, in extremis, death. In the Dictionnaire de musique, Rousseau claims that Swiss mercenaries were forbidden from singing their Swiss songs so as not to exacerbate their nostalgia. By the 19th century, nostalgia had become a topos in Romantic literature, inspiring a fashion for alpinism among the European cultural elite.
Today, nostalgia is no longer looked upon as a mental disorder, but as a natural, common, and even positive emotion, a vehicle for travelling beyond the deadening confines of time and space. Bouts of nostalgia are often prompted by feelings of <a href="https://www.psychologytoday.com/us/basics/loneliness">loneliness</a>, disconnectedness, or meaninglessness; thoughts about the past; particular places and objects; and smell, touch, music, and weather. When I was a child, I kept a lock of fur from my English sheepdog Oscar after he got run over by a tractor and had to be put down. Like the toys and books of our <a href="https://www.psychologytoday.com/us/basics/child-development">childhood</a>, or our childhood home, the lock became a sort of time portal, which, for many years, helped me to nostalgize about Oscar.
I say 'help' because nostalgia does have an unexpected number of adaptive functions. Our everyday is humdrum, often even absurd. Nostalgia can lend us much-needed context, perspective, and direction, reminding and reassuring us that our life (and that of others) is not as banal as it may seem, that it is rooted in a narrative, and that there have been-and will once again be-meaningful moments and experiences. In that much, nostalgia serves a similar function to anticipation, which can be defined as enthusiasm and excitement for some expected or hoped-for positive event. The hauntings of times gone by, and the imaginings of times to come, strengthen us in lesser times.
It is a strange thing: a vivid <a href="https://www.psychologytoday.com/us/basics/memory">memory</a> from the distant past, haunted by people who have grown up or grown old or are no more, doing things that are no longer done in a world that no longer exists. And yet it all seems so vivid in our minds that we can still picture the glint in their eye or the twitch in the corner of their mouth. Sometimes we even say their names under our breath as if that could magically bring them back to us. Nostalgia is nothing if not paradoxical. In supplying us with substance and texture, it also reminds us of their lack, moving us to restoration. Unfortunately, this restoration often takes the form of spending, and marketers rely on nostalgia to sell us everything from music and clothes to cars and houses. Many of our social connections endure solely or mostly out of nostalgia, so much so that inducing or sharing in a nostalgic moment can at once revive a flagging relationship. Nostalgia is more frequent in uncertain times and times of transition or change. According to one study, it is also commoner on cold days or in cold rooms, and makes us feel warmer!
On the other hand, it could be argued that nostalgia is a form of <a href="https://www.psychologytoday.com/us/basics/deception">self-deception</a> in that it invariably involves distortion and idealization of the past, not least because the bad or boring bits fade from memory more quickly than the peak experiences. The Romans had a tag for the phenomenon that psychologists have come to call 'rosy retrospection': memoria praeteritorum bonorum, 'the past is always well remembered'. If overindulged, nostalgia can give rise to a utopia that never existed and can never exist, but that is pursued at all costs, sapping all life and joy and potential from the present. For many people, paradise is not so much a place to go to as the place they (think they) came from. 
Nostalgia ought to be distinguished from homesickness and from regret. Although homesickness is a loan translation of nostalgia, it refers more specifically to the distress or impairment caused by an actual or anticipated separation from home. Regret is a conscious negative emotional reaction to past actions or lack thereof. Regret differs from disappointment in that regret is of actions, disappointment of outcomes. <a href="https://www.psychologytoday.com/us/basics/guilt">Guilt</a> is deep regret for actions because they fell short of our own moral standards. Guilt is a prerequisite for remorse, which is more mature and proactive than guilt in that it also involves an impulse for repentance and reparation.
Nostalgia can more fruitfully be compared with a number of similar or related concepts including saudade, mono no aware, wabi-sabi, dukkha, and Sehnsucht. Saudade is a Portuguese and Galician word for the love and longing for someone or something that has been lost and may never be regained. It is the desolate incompleteness or wistful dreaminess that can be felt even in the presence of its object, when that presence is threatened or incomplete-as, for example, in the famous final scene of Cinema Paradiso. The rise of saudade coincided with the decline of Portugal and the yen for its imperial heyday, a yen so strong as to have been written into the national anthem: Levantai hoje de novo o esplendor de Portugal ('Let us once again lift up the splendor of Portugal').
The literal translation of the Japanese mono no aware is 'the pathos of things'. Coined in the 18th century by Motoori Norinaga for his literary criticism of the Tale of Genjii, it refers to a heightened consciousness of the transience of things coupled with an acute appreciation of their ephemeral beauty and a gentle sadness or wistfulness at their passing-and, by extension, at the realization, reminder, or truth that all things must pass. Although beauty itself is eternal in its recurrence, its particular manifestations are unique and special because they cannot in themselves be either preserved or recreated.
Related to mono no aware is wabi-sabi, an aesthetic of impermanence and imperfection rooted in Zen Buddhism. Wabi-sabi calls upon the acceptance and espousal of transience and inadequacy to foster a sense of serene melancholy and <a href="https://www.psychologytoday.com/us/basics/spirituality">spiritual</a> longing, and, with it, liberation from the material and mundane distractions of the everyday. Hagi pots with their pockmarked surfaces, cracked glaze, and signature chip are an embodiment of wabi-sabi. With age, the pots take on deeper tones and become even more fragile and unique. Haiku poems with that evoke transience and loneliness are another paradigm of wabi-sabi.
The Buddha is reputed to have said, "I have taught one thing and one thing only, dukkha and the cessation of dukkha." That dukkha, or 'suffering', is inherent in all life is the first of the Four Noble Truths of Buddhism. The second Noble Truth is that the cause of all suffering is lust in the extended sense of coveting or craving. The deepest form of dukkha is the feeling of dissatisfaction that things, being impermanent and insubstantial, can never measure up to our standards or expectations. Once we have grasped this truth, we stop craving and stop struggling in hope and <a href="https://www.psychologytoday.com/us/basics/fear">fear</a>, and open ourselves up to the ways of the world. We still suffer, but the sting in our suffering has been removed because we understand that, for want of better words, our dissatisfaction has little to do with us as independent agents.
Sehnsucht is German for 'longing' or 'craving'. It is dissatisfaction with an imperfect reality paired with the conscious or <a href="https://www.psychologytoday.com/us/basics/unconscious">unconscious</a> yearning for an ideal that comes to seem more real than the reality itself, as in the final lines of Walt Whitman's Song of the Universal:
<blockquote>
Is it a dream?/ Nay, but the lack of it the dream,/ And, failing it, life's lore and wealth a dream,/ And all the world a dream. 
</blockquote>
CS Lewis called Sehnsucht 'the inconsolable longing' in the human heart for 'we know not what'. In The Pilgrim's Regress, he describes the feeling as 'that unnameable something, desire for which pierces us like a rapier at the smell of bonfire, the sound of wild ducks flying overhead, the title of The Well at the World's End, the opening lines of Kubla Khan, the morning cobwebs in late summer, or the noise of falling waves.'
Lewis redefines this feeling as 'joy', which he understands as 'an unsatisfied desire which is itself more desirable than any other satisfaction', and which I sometimes think of-in the broadest sense-as our aesthetic and creative reservoir. The paradox of 'joy' arises from the self-defeating nature of human desire, which might be thought of as nothing more or less than a desire for desire, a longing for longing. In The Weight of Glory, Lewis illustrates this from the age-old quest for beauty:
<blockquote>The books or the music in which we thought the beauty was located will betray us if we trust to them; it was not in them, it only came through them, and what came through them was longing. These things-the beauty, the memory of our own past-are good images of what we really desire; but if they are mistaken for the thing itself they turn into dumb idols, breaking the hearts of their worshippers. For they are not the thing itself; they are only the <a href="https://www.psychologytoday.com/us/basics/scent">scent</a> of a flower we have not found, the echo of a tune we have not heard, news from a country we have not visited.</blockquote>
Neel Burton is author of <a href="https://www.amazon.com/Heaven-Hell-Psychology-Emotions-second-ebook-dp-B081BCJJT6/dp/B081BCJJT6/">Heaven and Hell: The Psychology of the Emotions</a> and other books.
Find Neel Burton on <a href="https://twitter.com/#!/NeelBurton">Twitter</a> and <a href="https://www.facebook.com/NeelBurton">Facebook</a> 
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Nostalgia is sentimentality for the past, typically for a particular period or place with positive associations, but sometimes also for the past in general, 'the good old days' of yore. At the end of André Brink's novel, An Instant in the Wind, the character of Adam memorably says, 'The land which happened inside us no one can take away from us again, not even ourselves.'

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