Hi! if i have what i think is benign paroxysmal positional vertigo--room spinning when i change position in bed from laying on back switch to right side-- how do i know if i have this or if it is or may be something more serious? could i have tumor?

Unlikely/get eval: Rare things rarely happen while common things (BPPV) commonly do. I suggest you see your doc for confirmation & treatment. There are things like the Epley maneuver that can resolve symptoms & these can either be done by a professional or you can be taught to do them at home.

See a physician : You may have accurately diagnosed yourself, but you won't find out whether you're right or have a tumor here. Your question is only the beginning of the diagnostic process, not the end. Best thing to do is see your PCP. (S)he may be able to treat you, or if indicated, refer you to a hearing & balance specialist.