Just saw this post. You are dealing with the exact symptoms that I had dealt with for years. The heart palpitations/fluttering just prior to having a BM. Sometimes you get a little dizzy as the poop gets nearer the end (rectum) as though it is pressing on some nerve or something. You're correct about being careful about certain movements, standing, bending, twisting, or reaching during this time. It can trigger an arrhythmia. Why are some of us so sensitive to this I don't know, but it can be a real challenge in dealing with the symptoms on a daily basis. I haven't found out what this is, but it seems a light diet, or certain foods (fruits/vegetables) doesn't matter. Once the poop get down in that lower area of the rectum, or side of the lower large intestine, we feel it more than others and our body's tend to react in a negative way with the palpitations and fluttering accompanied by the dizziness at times. Once I pass the BM, you like engaging in activity again. But during the onset, you can't even give a lecture during a meeting let alone do a physical activity.