Originally Posted by
Carbonfiberboy
And talk to a doctor. Sounds very much like it could be atrial fibrillation to me. Did you feel weaker at the high HR? I have two cycling friends with afib. Feeling weak may or may not happen. They both still ride just fine. If you drink coffee, quit and see if you still have the issue, or especially don't drink coffee before a ride.
I think this is good advice. I had some wierd sudden changes in HR, so got my MD to order a Holter monitor, which I wore while exercising to rule out anything of a malignant nature. Very easy to do.