We know a lot about what happens to the brain and body during sleep thanks to technologies for measuring electronic activity patterns across the brain. There are two distinct types of sleep: rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. Dreaming can occur in both NREM and REM sleep. The idea that dreams occur in a short burst of time is not generally supported. Why do we sometimes feel sleepy after lunch? What determines whether a person is a morning type or an evening type? How does light exposure effect sleepiness? What is melatonin? What happens if we don't get enough sleep?