How to treat a hand cramp?

Warm soaks: Hand cramps can occur for a number of reasons. Best initial treatment is to stop the activities that are provoking the cramping, rest the hand, and soak the hand in a tub of warm water. You want the temperature very warm, but not hot enough to burn. Rest the hand is the water for 5 minutes, then gently massage and stretch the fingers while in the water for 5 more minutes.

Stretch & evaluate: I would expect your name to be something more like carpe mannus rather than carpe diem. Spasms are generally relieved by slow and progressive passive stretching of the effected muscle. Spasms can be caused by a variety of reasons including electrolyte abnormalities, denervation, endocrinologic diseases, seizure, nerve compression, etc. If this recurs discuss with your primary care physician.