That's just what happened to me when I had vertigo a couple years ago. I got out of bed in the morning to go to the bathroom and fell over. I found I could lie on my side comfortably, but I couldn't sit up at all and needed help standing.
It happened every month for about four months, and each episode lasted about a week. My doctor blamed a persistent inner-ear infection. I used some motion-sickness patches, and that eased the spinning a bit, but the patches have their own side-effects -- blurry vision for one.