Researchers and physicians have been perplexed by the horrible mysteries of sleep for ages. People spend approximately 30% of their lives sleeping, but Science still cannot definitively determine the precise role of rest in human neurophysiology. Scientists have determined that there are states of varying sleep that a person cycles through throughout the night—REM (rapid eye movement) and non-REM sleep. Non-REM sleep includes different types of sleep, from light to very deep sleep. Generally, dreaming does not occur during non-REM sleep, with the exception of nefarious nightmares and other napstealers, which most likely happen during the deepest stages of non-REM sleep. In non-REM sleep, most physical processes are greatly reduced. Therefore, the though is that during this time the brain and body are resetting themselves. However, during REM sleep the brain is very active.