By: Joann Bally CSCS

The normal sleep cycle goes in and out of several stages during the course of the night, no matter when you go to bed. These are identified by changes in brain waves.

A typical young adult who is a good sleeper and is sleeping 7 hours will go through the stages similar to the way described here.

Stage 0 is wakefulness with eyes closed. The sleeper is still awake but very relaxed, with brain waves showing alpha rhythms, often associated with meditation. In 15 minutes or less, he enters stage 1, and the alpha rhythms cease. Rather quickly he will go on to stage 2, which sees the beginning of delta brain waves. Stages 1 and 2 are called light sleep, and the sleeper can be awakened fairly easily. He then progresses to stage 3 and stage 4, which together are called deep sleep, or slow wave sleep. It is difficult to wake up from these stages.

After a relatively short time, our sleeper comes back up to stage 2, and then enters REM (rapid eye movement) sleep, where most dreaming takes place. Deep sleep occurs about an hour after falling asleep, and REM sleep first appears about 90 minutes into sleep. These 90-120 minutes cycles of REM and non-REM (stages 1-4 together) alternate throughout the night.

Slow wave sleep predominates through the first third of the night and is pretty much gone during later cycles. This is when the body repairs itself, and the brain wants to make sure it gets in. REM sleep predominates during the last half of the sleep cycle, with REM episodes getting longer closer to wake-up time. Brain waves during REM are similar to stage 1. The brain seems to use REM to consolidate and arrange new information from the previous day. There are no apparent serious health problems from lack of REM sleep, but not getting deep sleep can make you sick. (Your eyes really do move during REM sleep.)

Our good sleeper will spend 50% of his sleep time in stage 2 sleep, 20-25% in REM, maybe 5% in stage 1, which is mostly transition, and about 15% in deep sleep.

When you take a nap, limit it to 20-30 minutes so you can wake up out of light sleep. If you nap for an hour, you may be in slow wave sleep and it will be difficult to wake up.