Normal sleep consists of cycles of non-rapid eye movement (NREM) sleep alternating with rapid eye movement (REM) sleep. NREM sleep consists of light sleep and deep sleep. REM sleep is also known as “dream” sleep. The function of sleep is believed to be restorative, a time of rest and repair for the body.

Normal adults need an average of 8 hours of sleep (range 6 – 10 hours). It is normal to fall asleep within 10 to 20 minutes of going to bed, to wake up spontaneously once or twice in the night then fall back to sleep readily, and wake up feeling refreshed. Children need more sleep and tend to have more deep sleep, while the elderly have more frequent awakenings and less deep sleep.