Sleep Cycle

**Lasts about 90-110 minutes.

A person cycles through these stages multiple times (4-6x) throughout the night:

NREM 1 (1-5 mins) — Hypagonic stage

This is a very light sleep stage, where you're easily woken up. You might experience muscle twitches as your body begins to relax, and your heartbeat, eye movements, brain waves, and breathing activity begin slowing down.

• Alpha waves: a low-frequency brain wave associated with a relaxed wakefulness state.

NREM 2 (10-20 mins) — “Baseline” of sleep

This is the second sleep stage. During this stage, your brain waves slow down, including a drop in temperature, relaxed muscles, slowed breathing, and heart rate.

NREM 3 (15-30 mins) — Deepest sleep

This is the stage where you enter deep sleep. This stage is important for recovering/regenerating the body and brain. Growth hormones get released to repair our tissues, muscles, and bones. Additionally, it helps regulate our blood pressure and breathing rate. — Without enough stage 3 sleep, you feel tired and drained even if you slept for a long time. That’s why your body automatically tries to get as much stage 3 sleep into your sleeping period as early as possible.

REM (25% of your total time asleep) — Rapid eye movement

During this stage, brain activity increases, similar to waking levels. Your breathing and heart rate increase, eye movements become rapid, you start dreaming, and your limbs become temporarily paralyzed to prevent you from physically reacting to your dreams. Additionally, the brain turns your short-term memories into long-term memories. — Occurs between each cycle and increases in length as night’s sleep progresses.

• Rem Rebound: a temporary increase in the amount of time spent in REM sleep after sleep disturbance(s).

• Benefits: cognitive functions like learning, memory consolidation, and mood regulation, and overall health.

**Sleep paralysis typically occurs during the transition between REM sleep and wakefulness.

• Beta waves: a high-frequency brain wave associated with alertness, focus, and active mental processing during wakefulness.

Sleep inertia: a temporary state of drowsiness, grogginess, and impaired cognitive function that occurs immediately after waking up from sleep.

— “half-asleep”

Sleep Disorders

Sleep Apnea: a sleep disorder that irregular breathing while asleep

• Causes: airway obstruction, obesity, high blood pressure, hypothyroidism

• Symptoms: daytime sleepiness, loud snoring, gasping for air during sleep

Insomnia: inability to fall/stay asleep (due to stress or anxiety)

Narcolepsy: a type of hypersomnia — a neurological disorder that causes sudden “sleep attacks” — an uncontrollable urge to sleep, sometimes even without warning.

Somnambulism: sleep-walking (NREM3)