The different stages of sleep
Our sleep cycle is divided into four stages. The first three stages are called NREM (non-rapid eye movement) sleep and the last stage is called REM (rapid eye movement) sleep. Here's what happens during the different stages
- Stage 1 NREM: This is the first stage, which consists of light sleep and represents the transition between wakefulness and sleep. Your muscles relax and your heart rate drops, your breathing slows down and your eye movements decrease, as well as your brain waves, which are more active when you are awake, begin to calm down. The first stage usually lasts a few minutes.
- Stage 2 NREM: This stage of NREM sleep is characterised by deeper slumber as your heart rate and breathing rate continue to drop and your muscles relax. Your body temperature drops and your eye movements stop. Brain waves are also slow, except for a few occasional bursts of higher frequency electrical activity. Stage 2 is usually the most restful of the four sleep stages.
- NREM stage 3: This stage is crucial for you to feel rested and awake the next day. Muscles are as relaxed as they can be, and heartbeat, breathing and brainwave activity are all at their lowest levels. This stage begins with a longer duration and gradually shortens during the night
- REM stage 4: About 90 minutes after you fall asleep, you enter the first REM stage. Your eyes will travel rapidly back and forth under your eyelids, as the term suggests. Your breathing rate, heart rate and blood pressure will begin to rise. Dreams usually occur during REM sleep, and your arms and legs become paralyzed, which is believed to be to prevent you from physically carrying out your dreams. As the night progresses, the length of each REM sleep cycle increases. Memory consolidation, the process by which newly learned experiences are converted into long-term memories, has also been linked to REM sleep in a number of studies. As you get older, the length of the REM stage decreases, forcing you to spend more time in the NREM stages.
These four stages repeat cyclically throughout the night until you wake up. For most people, each cycle lasts about 90-120 minutes. NREM sleep makes up about 75-80% of each cycle. You may also wake up briefly during the night but not remember the next day. These episodes are known as "W" stages.