NREM Stage 1
Your body and mind go from being awake to being asleep at the start of sleep.
If someone wakes up at this point, they might say they weren’t sleeping.
The following things happen during stage 1 sleep:
Things stop working in the mind.
Because of this, your heart rate, breathing, and eye movement all slow down.
Your muscles may twitch as your body rests.
This kind of nap usually lasts between five and ten minutes. Theta waves are slow brainwaves that mostly happen in the frontal lobe and show that the brain is still working.
NREM Stage 2
Stage 2 of non-rapid eye movement (NREM) sleep lasts around 20 minutes per sleep cycle, and accounts for nearly half of overall sleep time.
Stage 2 sleep is characterized by the following:
You stop paying attention to what’s going on around you.
Your core temperature begins to decline.
You are unable to blink.
Your heart rate and breathing pattern stabilize.
The brain also starts to produce sleep spindles, which are bursts of rapid, rhythmic brain wave activity. Memory consolidation, the process through which your brain compiles, processes, and sorts information learned the day before, is thought to have a role in these.
During this time, your body’s natural rhythms are slowing down in preparation for NREM stage 3 sleep and REM sleep, the deep sleep stages during which the brain and body recover, repair, and reset in preparation for the next day.
NREM Stage 3
Deep, slow brain waves known as delta waves begin to emerge during NREM stage 3 sleep—a stage that is also referred to as delta sleep. This is a period of deep sleep where any environmental noises or activity may fail to wake the sleeping person.
Sleepwalking typically occurs during NREM stage 3 sleep. It is more common in the early part of your night’s sleep. Children and young adults are more likely to sleepwalk than older adults.
During NREM stage 3 sleep:
- Your muscles are completely relaxed
- Your blood pressure drops and breathing slows
- You progress into your deepest sleep
During this deep sleep stage, your body starts its physical repairs. Getting enough NREM stage 3 sleep makes you feel refreshed the next day.
Meanwhile, your brain consolidates declarative memories—for example, general knowledge, facts or statistics, personal experiences, and other things you have learned.
Stage 4: REM Sleep
While your brain is aroused with mental activities during REM sleep, the fourth stage of sleep, your voluntary muscles become immobilized.
During REM sleep, your brain’s activity most closely resembles its activity during waking hours. However, your body is temporarily paralyzed—a good thing, as it prevents you from acting out your dreams.
REM sleep begins approximately 90 minutes after falling asleep. At this time:
- Your brain lights up with activity
- Your body is relaxed and immobilized
- Your breathing is faster and irregular
- Your eyes move rapidly
- You dream
Like stage 3, memory consolidation also happens during REM sleep. However, it is thought that REM sleep is when emotions and emotional memories are processed and stored.
Your brain also uses this time to cement information into memory, making it an important stage for learning.
The American Academy of Sleep Medicine and the Sleep Research Society say that people need at least seven hours of sleep each night. On the other hand, good sleep that includes all four stages is important for your health as a whole.
Make an appointment with your doctor if you still have any of the following symptoms, as they may be signs that you aren’t getting enough sleep.
At least three nights a week, you have trouble going to sleep or staying asleep.
How you go about your day changes based on how tired you are.
It’s not unusual to feel like you need a nap in the middle of the day to keep going.
Someone who sleeps with you has told you that you snore or gasp while you’re asleep.
Your mental health is getting worse because you don’t get enough sleep.