This may be a silly question, but if you feel like that why not just start guzzling water? Wouldn't it soak in pretty quick and stop the cramping? I have little idea how these things work.
Sadly, I think it depends which way you've gone with the diuretics. Someone cleverer than me can explain, but as I understand it, what you drink needs to either contain sodium or potassium to 're-balance' what you've screwed up (see Dioralyte). And because these electrolytes are used to stop/re-start the heart during surgery, adding the wrong one can just make matters worse