Consciousness and Sleep Basics
Your brain operates in different states of awareness throughout the day. These range from fully conscious (when you're actively paying attention) to preconscious (memories you can recall) to nonconscious (automatic bodily functions) and unconscious (when you're knocked out). We can also experience altered states through various means like drugs or hypnosis.
When you sleep, your brain cycles through distinct patterns of activity. While awake, your brain produces beta waves. As you get drowsy, these shift to higher amplitude alpha waves. Once asleep, you enter non-REM (NREM) sleep, which has three stages: light sleep (Stage 1), sleep spindles (Stage 2), and deep sleep with delta waves (Stage 3).
The most fascinating phase is REM sleep (Rapid Eye Movement), when most dreaming occurs. Your entire sleep cycle takes about 90 minutes, with REM periods occurring between cycles and lasting longer as the night progresses. If you don't get enough REM sleep, your body compensates with REM rebound - quick bursts of REM during daytime to make up for the loss.
Did you know? When you experience that weird falling sensation that jolts you awake as you're drifting off to sleep, you're experiencing a "hypnic jerk" - it happens during the transition from Stage 1 to Stage 2 sleep!