NREM Stage 1: The first stage of the sleep is a transition period between wakefulness and sleep. During this stage, your brain slows down as well as your heartbeat, eye movement and breathing. Your body relaxes and your muscles may twitch. This brief period of sleep lasts for around 10 minutes.
NREM Stage 2: Approximately 50% of the total sleep time consists of stage 2 sleep. During this stage you become less aware of your surroundings. Your body temperature drops, and eye movements stop. Breathing and your heart rate become more regular. Brain activity slows with short bursts of activity that help to resist being woken up by external stimuli. The short bursts of brain activity are known as sleep spindles and are thought to help with memory consolidation. This cycle of sleep lasts approximately 10-25 mins in the first cycle, but this stage can become longer at different cycles through the night.
NREM Stage 3: This stage of sleep is known as deep sleep or delta sleep. Noises and activity may fail to wake a sleeping person in this stage of sleep. During this stage, your muscles are completely relaxed. Your blood pressure drops and breathing slows. This stage of sleep allows the body to recover and repair. There is evidence that deep sleep contributes to insightful thinking, creativity, and memory. This cycle of sleep mostly occurs during the first half of the night, commonly lasting 20-40 minutes.
REM Stage 4: REM sleep begins approximately 90 minutes after falling asleep. Brain activity picks up, nearing activity levels seen when awake. Even though the eyes are closed, they can be seen moving quickly. During this stage, your breathing becomes faster and irregular and you begin to dream vividly. Your body experiences temporary paralysis known as muscle atonia. The paralysis helps prevent you from acting out your dreams. Your brain will use this stage to cement information into memory and when emotion and emotional memories are processed and stored. This stage of sleep may only last a few minutes in the first cycle of sleep but progressively lengthens in time lastly for around an hour in the second half of the night. REM sleep makes up about 25% of sleep-in adults.
