Get Ready: Sleep Stages

Sleep Stages

A helpful first step in developing healthy sleep is to have some basic information about sleep.

When we sleep, we go through different types of sleep or stages of sleep. We repeat the stages of sleep over and over again during the night. Information about the stages of sleep comes from research. Scientists have studied persons sleeping overnight in sleep laboratories and hooked up to monitoring equipment.

Good sleepers fall asleep easily but typically in not more than 30 minutes. After we fall asleep, we start stage N1 of sleep, a very light sleep. This is a transition or bridge stage which means the stage between wake and sleep. It is the 'drifting off to sleep' stage. If you were awakened from stage N1 sleep, you would probably say you had not been sleeping. After stage 1, we enter stage N2 of sleep, still a light stage of sleep but more sound than stage 1. If you were awakened from stage N2 sleep, you would probably say you had been asleep. We then move into stage N3 of sleep. Stage N3 is the deepest sleep. It takes more effort to awaken someone from stage N3 sleep than the other stages. After stages N1-N3, we enter the REM stage of sleep (rapid eye movement sleep) which is often called 'dream sleep.'

We spend different amounts of time in the different stages of sleep, depending on the time of night. We have more deep sleep or stage N3 in the first half of the night's sleep and less as the night goes on. We have more REM or dream sleep in the later half of the night.

What happens to our sleep as we age?

As we age, we start to have less deep sleep (stage N3) so we tend to stay in lighter stages of sleep (stages 1 and 2). This is one reason why older persons may wake up more often. They spend more time in lighter sleep stages so they are more vulnerable to awakening. Older persons often wake up earlier than younger sleepers. The duration of sleep may be shorter than when we were younger. Our sleep can be affected by changes in our health as we age such as diabetes, arthritis, and prostate enlargement.

How is sleep regulated?

Two factors work together to regulate sleep: the sleep drive and the biological or internal clock. One way to understand the sleep drive is to think about another drive, the drive to eat. If we woke up in the morning and did not eat all day, at dinner time we would be very hungry. A similar process occurs with sleep. After we awaken in the morning, the longer we spend awake, the greater is our drive to sleep. At the end of the day, we're sleepy. Our drive to sleep is high because we've been awake all day: we have built up a big sleep debt! We pay off the sleep debt during the night as we sleep. When we awaken in the morning, our drive to sleep (sleep debt) starts to build again throughout the day. Persons with insomnia develop poor sleep habits that can interfere with the drive to sleep.

The other factor that helps to regulate our sleep is our biological or internal clock. People and animals have a very strong internal clock that helps to regulate many body functions such as blood pressure, heart rate, urine production, digestion, temperature, and sleep-wake rhythm. In order to keep our internal clock set and running smoothly, it needs signals from the environment such as light and dark, regular schedules and activities, and social interactions. Having the same wake-up time every day is one of the strongest signals we can give our internal clock to strengthen our sleep-wake rhythm. Persons with insomnia develop poor sleep habits that can interfere with the signals that our internal clock needs to keep sleep and wake balanced.

Updated January 2012
Clinical Advisory Board Sponsors: Karen M. Ott
Clinical Subject Matter Experts: Dr. Dana R. Epstein, Dr. Gail Powell-Cope, Dr. Joseph V. Agostini, Dr. Monica S. Horton
Patient Education Subject Matter Experts: Eileen Canzonetti, Karen M. Ott, Patricia Jost