Feeling sick is an emotion meant to help you get better faster

• In order to avoid additional infections or injuries that would increase the immune system's energy requirements, your body increases sensitivity to nausea and pain.
• Sensitivity to cold motivates you to find warm clothing and heat sources that reduce the costs of keeping your body temperature up.
• Changes in your appetite and food preferences push you to eat in a way that supports your body.
• Feeling miserable provides a signal to your family that you need help.

People possess a regulatory program that lies in wait, scanning for indicators that infectious disease is present. If it detects signs of infection: 

• The program sends a signal to various functional mechanisms in the brain and body.
• In turn, they change their patterns of operation in ways that are useful for fighting infection.
• These changes together produce the experience of being sick.