Sleep cycles are patterns of brain activity and physiological changes that occur during sleep.
The two main types of sleep are Rapid Eye Movement (REM) sleep and Non-Rapid Eye Movement (NREM) sleep.
Each cycle consists of different stages of sleep, and they typically repeat several times throughout the night.
Here's a breakdown of the different sleep cycles and what a person might experience during each one:
1. NREM Stage 1 (N1):
- This is the lightest stage of sleep.
- During N1, you may feel like you are drifting in and out of consciousness, and you might experience sudden muscle contractions known as hypnic jerks. Most people have experienced these at one time or another. They are not harmful and are pretty common.
- You can be easily awakened during this stage, and it generally lasts for a few minutes until you go into the slightly deeper stage 2 sleep
2. NREM Stage 2 (N2):
- During this stage your brain starts producing what are called sleep spindles and K-complexes during N2, these are thought to protect sleep from being disrupted by external stimuli. It would appear that as people age sleep spindles occur less frequently which might be part of the reason older people wake from sleep more often .
- During this stage your breathing and heart rate become more regular, and your body temperature drops.
- You may feel somewhat unaware of your surroundings, but you can still be easily woken up.
3. NREM Stage 3 (N3) or Slow-Wave Sleep (SWS):
- N3 is the deepest stage of NREM sleep, also known as slow-wave sleep (SWS) because of the slow brain waves observed.
- This is the most restorative stage of sleep, and it's important for physical recovery and memory consolidation.
- During N3, you may feel disoriented if you are awakened and you might experience a feeling of grogginess for a short time after waking up.
4. REM Sleep:
- REM sleep is characterised by rapid eye movements, increased brain activity, and vivid dreams.
- This stage is essential for emotional regulation and memory processing.
- Your muscles are typically paralysed during REM sleep to prevent acting out dreams.
- If you are awakened from REM sleep, you may have a more vivid recall of your dreams
This sleep cycle typically progresses in the following order: N1 -> N2 -> N3 -> N2 -> REM.
Each cycle lasts around 90 to 120 minutes, and as the night progresses, the proportion of REM sleep increases while N3 (deep sleep) decreases.
Each cycle after the first cycle usually goes through N2>N3>REM
Throughout the night, you will usually go through multiple sleep cycles, and each cycle contributes to your overall restfulness and well-being.
Disruptions in sleep cycles due to various factors like hot sweats, stress, caffeine intake, or certain sleep disorders like restless legs and sleep apnoea can impact the quality your sleep and lead to feelings of fatigue and irritability during the next day.
