as needed medication?

I have POTS, and am starting to look into medication. Is there such thing as an “as needed” medication? I have good days and bad days. My POTS is mild and can be controlled through water, electrolytes, etc, but when I have a bad day it is horrible. The bad days are random too, sometimes it will happen a couple times a week, other times it won’t happen for 2-3 weeks. I was wondering if there was a medication I could take on those bad days, rather than taking something everyday.

I always get scared starting medications, and after reading up on some of the meds it makes it worse. I do not need my heart rate or bp significantly lowered everyday, some days it is normal. Because of this I don’t want to take something everyday.

TIA