All of us have experienced it before: the moment when the awful wailing of your 6:00 AM alarm blasts your eardrums like the enraged cries of a cat being bathed. The valiant battle waged between willpower and the delusional belief that “just five more minutes” of sleep won’t hurt. The agonizing death of your soul as you part with blankets so toasty and warm and soft, it is like you are cuddling with a panda.

Sleep deprivation hurts. But its pain is understandable and expected.

What is baffling is the fatigue that accompanies seven, eight, or even ten hours of sleep. Even more perplexing is a seemingly magical ability to feel energized even with three measly hours of sleep. It just doesn’t make any sense. But the world is not conspiring against you – I promise.

One fateful day in AP Psychology elucidated all these years of confusion with a simple but ingenious explanation. When you sleep, you rotate through numerous 90-minute long sleep cycles, with each cycle is comprised of five distinct stages. Stage 1 occurs when you first fall asleep. It is light sleep, easy to wake up from. With each stage, you progressively fall into deeper and deeper sleep, eventually reaching Stage 4 and REM sleep, the most difficult stages to wake up from. During Stage 4, yours brain emits slow brain waves called delta waves, and then gives way to the dreaming stage: REM sleep.

The problem occurs when your alarm clock rings right as you are in the stages of deeper sleep. The ensuing grogginess and utter misery is inevitable; it’s your body admonishing you for taking away its most valuable resting period.

My advice? Simple: sleep in multiples of 90 minutes. Be it three hours or six hours or nine hours, when you awake, you will be ready to take on the day.