What are the phases of sleep?

Sleep is typically divided into two broad types: Non-Rapid Eye Movement (Non-REM) sleep and Rapid Eye Movement (REM) sleep. Here’s a breakdown of the sleep stages:

1. Non-REM Sleep:

   • Stage 1: This is the lightest stage of sleep, often considered a transition phase between wakefulness and sleep. It features slow eye movements and reduced muscle activity.
   • Stage 2: Still classified as light sleep, this stage includes occurrences of sleep spindles and K-complexes. These are rapid brain activities that help prevent awakening by sensory input.
   • Stage 3 and 4 (Deep Sleep): These stages are progressively deeper stages of sleep, characterized by slow brain waves known as delta waves. Deep sleep is crucial for physical recovery and aspects of memory and learning.

2. REM Sleep:

   • This stage occurs approximately 90 minutes after falling asleep. It's characterized by rapid eye movements, increased brain activity, paralysis of major voluntary muscles, and vivid dreams. This stage is important for emotional regulation and forming certain types of memories.

The succession of Non-REM and REM sleep across the night forms sleep cycles, each lasting about 90 minutes. Typically, deeper Non-REM sleep dominates earlier in the night, while REM sleep periods extend as the night progresses 1 2 3.