This is Dr. David
can you reschedule your massage?
you should try some Immodium to see if that helps your diarrhea symptoms.
you need to drink more fluids and gadoade fluids and electrolyte fluids if possible.
I take it you are worried about needing to have diarrhea during your massage.
massage can be good to relax your muscles.
but it most likely won't help your stomach bug or diarrhea symptoms.
ask the hotel concierge to see where you can buy some immodium or medication for travelers diarrhea.
I'm sure the concierge will be able to help you
and ask where you can buy some sports drinks or electrolyte drinks.
eating foods like bananas can help bind you up so you don't have so much diarrhea as well.
I hope you are able to have a trip tomorrow.
try the massage.
if you don't like it or have urgency for diarrhea during the massage, you can always ask to be excused.
let me know if you have other questions.