Sleep occurs in five stages: wake, N1, N2, N3, and REM. Stages N1 to N3 are considered non-rapid eye movement (NREM) sleep, with each stage representing different brainwave activity and physiological changes.
- Stage 1 (N1): This is the lightest stage of sleep and is characterized by a transition from wakefulness to sleep. Brain waves become slower, heart rate and breathing slow down, and muscle activity decreases. This stage usually lasts only a few minutes and makes up about 5% of your total sleep time.
- Stage 2 (N2): This stage is characterized by deeper sleep with further slowing of brain waves, a decrease in heart rate and breathing, and reduced muscle activity. This stage accounts for about 45-55% of total sleep time.
- Stage 3 (N3): This is the deepest stage of sleep, also known as slow-wave sleep (SWS) or delta sleep. Brain waves are very slow and large, and the body is very relaxed. This stage is important for physical restoration and memory consolidation and comprises about 20-25% of total sleep time.
- REM (Rapid Eye Movement) Sleep: This stage is characterized by rapid eye movements, increased brain activity, and muscle paralysis. This stage is associated with dreaming and emotional processing. REM sleep accounts for about 20-25% of total sleep time.
The sleep cycle typically lasts around 90-110 minutes and repeats throughout the night. As the night progresses, REM sleep stages become longer and deeper, while NREM stages, particularly N3, become shorter.
Note: While there are five stages of sleep, it's important to understand that the distinction between NREM stages 3 and 4 is sometimes blurred. Some sources consider them as one stage (N3), and others separate them into two distinct stages.
