my heart flops like a fish in my chest

Don't know about how much is pain or just stomach and general discomfort/worry, but I do recognize the 'floppy' sensation. My personal diagnosis was something called Bigeminy. You might want to talk to your doctor because it can be or become serious.  Also, if that's what your experiencing, the bigeminy, here's a quote from Joel Braunstein, MD, of Johns Hopkins University and Joseph Toscano, MD:  "All of us at one time or another experience occasional premature heartbeats.  In isolation, these are not usually reason for concern.  It is useful, however, to have an understanding of what can precipitate premature heartbeats, including bigeminal heart rhythms.  Increasing age, tension, anxiety, overeating, exercise, and stimuants such as caffeine, tobacco, alcohol, and over-the-counter decongestants are all associated with greater frequency of premature heartbeats....   ....Finally, various forms of cardiovascular disease always need to be considered whenever you have any type of irregular heartbeat.  Premature ventricular beats may occur after suffering a heart attach or having compromised overall heart function, which occurs in the setting of heart failure.  Premature beats in these settings need to be evaluated carefully because that can signal a person at high risk for experiencing sudden cardiac death....     .....In the absence of identifiable causes, premature beats, including bigeminy, are not typically treated.  If a predisposing factor can be identified, treating or eliminating the predisposing factor usually reduces or eliminates the abnormal heart rhythm..."

Hope this helps you make a wise decision.  I got this information from healthcentral.com when I Googled the word Bigeminy.  Take care, barb, & God bless.

Merrilee