Why do humans need sleep?
Unfortunately, the scientific community isn't totally in agreement as to why humans need sleep. Our best guess is that sleep offers the body a chance to restore and rejuvenate as well as process memory.
Restful sleep allows the body to focus on just the basic and vital functions of breathing, pumping blood, and repairing or generating new cells and tissues. When we're awake throughout the day, we are spending our bodily energies on other activities like walking, working, and thinking. Sleep is a break for both body and mind, allowing our energy to be directed towards maintaining a healthy body.
Neurologists also feel sleep is a time for our brains to process all of the short-term memories acquired during the day, "sort" through them, and decide what should be processed into long-term memory. This is a possible reason behind why dreams often contain some of the things we've done or thought about or people we've seen during the day.
It's very important to get enough sleep so your body has a chance to perform these restorative maintenance functions. Most people need around eight hours of sleep, but depending on your age and activity level, you may need more or less than this. As long as you feel well-rested, you're probably getting enough sleep!