Sleep is not uniform. Instead, over the course of the night, our total sleep is made up of several rounds of the sleep cycle, which is composed of four individual stages.

In a typical night, a person goes through four to six sleep cycles. Not all sleep cycles are the same length, but on average they last about 90 minutes each.

It is normal for sleep cycles to change as we progress through our nightly sleep. The first sleep cycle is often the shortest, ranging from 70-100 minutes, while later cycles tend to fall between 90 and 120 minutes. In addition, the composition of each cycle — how much time is spent in each sleep stage — changes as the night goes along.

Sleep cycles can vary from person to person and from night to night based on a wide range of factors such as age, recent sleep patterns, and alcohol consumption.

One earlier misconception that has now been revised is that the body completely slows down during sleep; it is now dear that the body’s major organs and regulatory systems continue to work actively – the lungs, heart and stomach for example.

Another important part of the body also operates at night – the glands and lymph nodes, which strengthen the immune system. This is commonly why the body’s natural immunity is weakened with insufficient sleep.

Also in the brain, activity of the pathways needed for learning and memory is increased.

Our body requires less sleep the older we get.

Whilst, it is true that babies need 16 hours compared to 9 hours and 8 hours respectively for teenagers and adults, this does not mean that older people need less sleep.

However, what is true if that for a number of different factors, they often get less sleep or find their sleep less refreshing.

This is because as people age, they spend less time in the deep, restful stages of sleep and are more easily awakened. Older people are also more likely to have medical conditions that affect their sleep, such as insomnia, sleep apnoea and heart problems.

1. Non-REM sleep (sometimes called NREM), which includes light and deep sleep, accounts for about the majority of our sleeping time.

2. REM (Rapid Eye Movement) sleep is where we may spend some of our time dreaming. This typically takes place during the last half of our night’s sleep.

While we’re snoozing, we usually go through 4-5 sleep cycles that begin in light NREM sleep and end in REM sleep with each cycle taking between 70 and 120 minutes to complete.

1. Light Sleep

• Stage 1 non-REM sleep – a person in this stage is between being awake and asleep or is in a state of very light sleep.
• Stage 2 non-REM sleep – this stage is characterized by a slightly deeper sleep. Body temperature drops and heart rate slows down.

2. Deep Sleep

• Stages 3 non-REM sleep – a state of deep and restorative sleep known as slow-wave sleep, or delta sleep. The muscles relax, the supply of blood to the muscles increases, and the body repairs and grows tissue. Hormones are released and energy stores are replenished.

• During REM sleep, our brain is almost as active as it is when we are awake.
• In this phase of sleep, breathing can become fast and irregular.
• REM sleep is thought to help consolidate memories.
• Drinking alcohol before bed reduces the amount of REM sleep we have.
• People with REM sleep behavior disorder act out their dreams.