 Deeper sleep, deepest sleep, and REM, or slow-wave sleep. That's the stage where you're most likely to wake up. And if you tend to go to bed at roughly the same time on a nightly basis, these cycles are roughly the same length, and you may wake up at the same time in the night. Now, remember this as a general rule. You sleep more deeply in the first half of the night, so you're more likely to wake up during the second half of the night. And, yes...