What Is Sleep?
Sleep isn't just "being unconscious" - it's a complex biological state where your body becomes less responsive to the world whilst undergoing major internal changes. Your brain activity, heart rate, breathing, blood pressure, and body temperature all shift dramatically as you move through different stages.
Your nightly sleep consists of multiple 90-120 minute cycles that repeat throughout the night. Each cycle takes you through the same sequence of stages, though the patterns vary depending on your age - teenagers actually have different sleep patterns compared to adults and elderly people.
Sleep divides into two main phases: Non-REM sleep (stages 1-4) where your body winds down and dreams are rare, and REM sleep (stage 5) where your brain becomes highly active and vivid dreams occur. Understanding these stages helps explain why some mornings you wake up feeling refreshed whilst others leave you groggy.
Quick Tip: Your sleep follows the same sequence every night: Stage 1→2→3→4→3→2→REM, then repeats!
