I've had something like this but it hasn't happened in years. It feels like something the size of a pebble exploding in the middle of my head. It never lasts longer than a fraction of a second and it's nothing I ever even think of asking a doctor about, but sometimes startling enough to make it hard to go back to sleep. It often seems to happen in lieu of that feeling like you're falling just as you're half asleep. I've never been on any psych drugs, though I was under a bit of stress when they would happen.