Humans are slow moving in comparison to most monster. And have you watched zombie movies? They're very odd. Zombies shamble slowly whenever they're on screen. Obviously, the rigor mortis has kicked in something awful. But they're always right behind the terrified fleeing human. I suspect they break out into an Olympic sprint whenever the camera panns off them.

The more you do it, the more control you get and the longer you can stay asleep. Nightmares are a really good time to figure out how to do it.