Why do we sleep?

Scientists have yet to determine exactly why people sleep but as we pass from young adulthood to middle age,we get less deep sleep and more light sleep.There is three different kinds of sleepb deep sleep,light sleep,and REM sleep.If you are a student you would want deep sleep so you can acually do work and not fall asleep.Did you know that you can live longer without food than you can without sleep.You need sleep to function.Also we sleep mostly when we should be working and when we should be sleeping we are working. The fact is we need sleep to function in the world.MAKE SURE YOU SLEEP GOOD.