Imagine yourself in the following situation: it's late. So late it's actually early. You're sound asleep under the warm, snuggly covers. You're in the middle of one of those sleepy roll overs where you're awake for like a half second as you get into an even more snuggly and comfortable position. All you hear is the soft breathing of your spouse next to you.
What was that? You snap to alertness for a split second before you chuckle to yourself. Nothing. Of course it was nothing! Probably some electronic device or the furnace or whatever cycling on or off. You glance at the clock: 4:25am. Perfect. You can probably snag another complete REM cycle before it's time to wake up. You close your eyes and begin to drift off.
And then you hear shit in your bathroom falling off the shelf and clattering around on the floor.