When I was in practice, I took care of patients with snoring and sleep apnea (where your blood oxygen drops and one actually wakes up). This is a good summary about sleep, its stages and why it’s important.
During an ideal night’s sleep, you go through several 90-minute cycles that sample each phase of sleep. Each cycle plays an essential role in maintaining your mental and physical health. The amount of each phase of sleep can vary significantly between nights and individuals.
Stages of Sleep
Sleep has been traditionally divided into two categories: Non-rapid eye movement (NREM) and rapid eye movement (REM). Both are exactly what they sound like–your eyes either remain still or move rapidly under your eyelids. Together, these two types of sleep make up a single cycle where your brain progresses sequentially through each stage of sleep: wake, light sleep, deep sleep, REM, and repeat.
Stage 0: Wake
Awake time is the time spent in bed before and after falling asleep. It also includes brief awakenings during the night. These episodes are completely normal for healthy adults.
Stages 1 & 2: Light Sleep
Light sleep initiates your sleep cycle and acts as a transition to deeper sleep stages. During this stage your muscles begin to relax, your heart rate and breathing slow down, and you wake up easily.
During light sleep, you can expect the following:
- muscles relax and may jerk
- respiration slows
- heart rate decreases
- body temperature drops
- sleep begins
Stages 3 & 4: Deep Sleep
Deep sleep focuses on your body. It is the most rejuvenating and restorative sleep stage, promoting muscle growth and repair as well as waste removal in your brain. In this stage, you have difficulty waking up and are disoriented or groggy if awoken.
During deep sleep, you can expect the following:
- blood pressure drops
- blood flow increases to muscles
- repair hormones (i.e. growth hormone) are released
- tissue growth and cell repair occurs
- long, slow brain waves
- brain flushes out waste
Stage R: REM Sleep
REM sleep is essential to re-energizing your mind. REM is associated with dreaming, memory consolidation, learning, and problem solving. The time spent in this sleep stage usually decreases with age.
During REM sleep, you can expect the following:
- respiration increases
- heart rate increases
- temperature regulation is switched off
- brain activity is high; vivid dreams may occur
- body becomes immobile