mestinon experiences?

hi everyone! i have POTS, ME/CFS, & gastroparesis. I’ve been prescribed Mestinon mostly to help with tachycardia/POTS. I’m VERY apprehensive and scared to take the mestinon, as every other med i’ve tried has gone awful. I’m very very med sensitive. Has anyone else in a similar boat tried it? Experiences? What to expect? TIYA!