In the past couple of months, I've woken up three time with a pounding heart - once a few weeks ago, and twice in the past week. In the most recent events, I've had a good night's sleep only to be woken around 5 or 6am with a heart rate that is 1-1/2x higher than normal (normal resting is 52bpm) and a lot harder than usual. It lasts for about 5-10 minutes, then is normal again. Accompanying the pounding is a sensation in my lower abdomen (once like a brick and once a bm). Drinking some water seemed to help. Also accompanying all of this is a somewhat intense anxiety. Has anyone experienced similar? It seemed to come out of the blue...

Some background: after a recent ecg (prelim for volunteer clinical study), I was told I had bradychardia and a first degree av block, but other than that, I exercise a couple times a week, eat decently (with some sweets, pizza, etc) and some caffeine (1-2 cups coffee/day). I am 35 years old.