When we close our eyes at bedtime, our brain activity changes as we go through different sleep stages or cycles. Each of these stages is essential for restful sleep, but it’s important to spend the right amount of time in each stage. Too much time spent in the light sleep stage leads to poor sleep and low energy levels the next day.
Let’s take a minute to go over the various stages included in the average sleep cycle, and the primary purpose of each one. The sleep stages can be divided into two main sleep categories: non-REM sleep (or NREM sleep), and REM sleep.
When you first drift off, you go immediately into stage 1 of non-REM sleep. Stages 1 and 2 of non-REM sleep are also known as light sleep. Here are some of the changes that happen in your body during the non-REM sleep stages:
- Stage 1: This is when your body transitions from being awake to being asleep. It lasts several minutes and is marked by a slowing of eye movements, heart rate, and respiration. During this sleep phase, the brain waves slow down and blood pressure drops.
- Stage 2: When your body enters stage 2 of non-REM sleep, your core temperature drops, brain waves continue to slow (with short bursts of increased activity), and eye movements stop. Most of us spend about 50% of the total sleep cycle in stage 2 sleep. It is possible to dream during this stage, though non-REM dreams are not as vivid as dreams that occur during REM sleep.
- Stages 3 and 4: This is when the body first enters into deep sleep. During these stages of slow wave sleep, brain waves become the slowest they’ll be throughout the sleep cycle. Heart rate and breathing also slow down substantially and the muscles relax. This is when we experience the most restorative sleep. Stage 3 of slow wave sleep usually lasts between 45 and 90 minutes. It tends to become shorter with each sleep cycle you experience throughout the night.
Each period of non-REM sleep is followed by a period of REM sleep. Approximately every 90 minutes, the cycle is repeated in people with normal sleep patterns.
Some of us have one or more sleep disorders that may prevent us from spending adequate time in one or more of the sleep stages. Often, people with poor sleep quality don’t spend enough time in deep sleep/slow wave sleep. The brain needs to get enough time in slow wave sleep or it may not function optimally the next day.
Rapid Eye Movement (REM) sleep occurs after you get through the non-REM phases of your sleep cycle. It consists of the following single stage:
- Stage 5: During the REM stage of sleep, breathing becomes faster and may even be irregular, the limbs may become paralyzed, and the heart rate increases until it’s almost as fast as it is when you’re awake. The eyes rapidly move from side to side and this is when vivid dreams occur.
All these stages of sleep have their unique purposes, and it’s important to spend adequate time in each one.