Just barely not falling asleep
Think of that feeling you have right before you fall asleep. Your eyes are closed, your mind is drifting, and you can just barely start to feel your consciousness start to slip away.
Try it now. Close your eyes and let your whole self relax. Let your mind relax until it’s barely working, and starts to drift off.
This will be hard if you’re wide awake, but it’ll be easy if you’re exhausted. And it’s surprising how refreshing it can be, even just for a few seconds, to really, deeply relax your whole self.