Is it appropriate to ask a professor about continuing my degree?
To me it never hurts to discuss possible options. Complex mathematics can be a difficult hurdle to cross and it seems you're making a leap from basic math to university-level math without being prepared for it. 

Explain your situation in detail. I'm sure this isn't a first for the head of your department and maybe (s)he can suggest some courses which might help you in catching up with the program.

I'd keep your high blood pressure problem out of the discussion.