Sleep time is the time for the brain to rest and to remember the activities that took place that day. When you stay up late, you're increasing the amount of information to keep in mind while reducing your brain's resting time. The rate of memory decline in people who have a habit of staying up late is therefore 5 times higher than that of the average person. So remember to make sure your brain gets enough rest for 8 hours a day. During sleep, especially the time frame from 12 pm to 4 am is the time when the body releases the hormones necessary for maintaining the body's immunity. Staying up late often will cause these hormones to be missing or completely disrupted if you stay up until morning. So people who stay up late are more likely to get diseases like the flu and allergies than people who get adequate sleep.