I am 43 years old, 140lbs, 5'9", run 60-70 miles per week. About 3 weeks ago, I suffered from 60-hour diarrhea, which I finally controlled with immodium. I did not run for a few days and then tried a very easy 7.5-mile run. On the last mile or two, I felt extremely exhausted. My heart rate was elevated (about 15-20 bpm higher than normal). I attributed this to the aftermath of the diarrhea. Nevertheless, I stopped running and exercising for about 2 weeks.
2 weeks later, I tried to run very easy again, but stopped after about 2.5 miles. HR was again about 15-20 bpm higher than normal, peaked at about 88% of my maximum heart rate. Everything else felt normal. It certainly did not feel like running at my anaerobic threshold. After the run I felt my pulse, which turned out to be abnormal. For about 2 or 3 minutes after the run, I felt 3 beats, then a break, 3 beats, break, sometimes 2 beats, break. While this was happening, it slowly dropped from 180 to about 120. Although beating normally, the HR stayed at 100-120 bpm for at least an hour. Even though I never checked that before, I do not believe this is normal either.
I went to a cardiologist, but everything turned out normal. The EKG did not show any abnormalities. Blood pressure is low (90/58), resting heart rate slightly elevated (76 vs. 60) and I do sometimes feel a little dizzy after getting up from a chair. He told me I could get slowly back into running, but I do not really feel comfortable. Any suggestions?