I've been seizures free for 4years but still on medication until now. is there any risk of inhaling prosthetic crown for my rct molar tooth?

Highly unlikely: If your dentist takes appropriate precautions, it is highly unlikely that you would swallow your crown during the placement procedure, even if you were to have a seizure. Once in place, it is not meant to come off easily so there is no fear of swallowing it afterwards. A crown will only fall off by itself if something is really wrong, so make sure you keep up with your routine visits.

Low risk: The crown would have to be completely loose, but even so it probably would not be swallowed. See you Dentist for routine care, at least twice a year, during which time the integrity of your crown will be evaluated. Review your concerns with your Dentist. Even if loose crown is swallowed it should pass through your system uneventfully.