 A Better Life with Dr. Samjay Gupta. Why do you seem to wake up at the same time in the middle of the night every night? There's actually a pretty good reason for this, and it starts with something known as your sleep architecture. That's a fancy term for the four stages of sleep you cycle through every 90 to 120 minutes. Light sleep, deeper sleep, deepest sleep, and REM or slow wave sleep. That's the stage where you're most likely to wake up.