Years ago I played a gig in a restaurant from 6:30 pm to 10 pm with two 15-minute breaks. Watch that you are seated on the front half of the stool. Take many sips of water. Use your breaks off of the harp to walk around, do yoga stretches, totally relax but with movement to improve your circulation, and add more potassium to your diet, apricots, bananas, etc. The “little” break needs to be a full fifteen minutes and you deserve every minute of it. Hope it goes away! If there is an MD on board, consult with him/her.