After never feeling vertiginous in my life, I've had 4-5 episodes over the last 18 hours. I don't feel sick in any other respect. What's happening?

Possible BPPV. Short, less than one minutes of spinning with movement like rolling over in bed is likely benign paroxysmal positional vertigo or bppv. There are other types of vertigo as well. I recommend seeing an ENT who treats bppv with canalith repositioning maneuvers.