Last 3 days flutter/pounding heartbeat. last night woke with severe crampy sharp abd pain this am very watery forceful diarrhea. any possible cause?

Gastroenteritis: Gastroenteritis comes to mind. Causes include food poisoning, food intolerance, malabsorbtion, colitis, medicines, viral, emotional, and others. The cramps precede and predict the development of diarrhea as they reflect hyper-peristalsis. Fluttering, if related, may reflect low potassium that diarrhea causes. The timing, though, may not be right unless you had some diarrhea beforehand.