I purchased the book Chi Running and started reading it last night. I'm going to try and adjust my form to make myself more efficient and see if I can slow down without pain.

I think I may go ahead and get checked out by a doctor anyway. My mom has a heart problem that essentially causes her heart to misfire a bit (instead of going Ka Chunk, Ka Chunk, Ka Chunk, it just goes Ka, Ka, Ka, Ka) and her heart monitor reads her heart really fast. Blood is pumping, but not well. I wouldn't be surprised if I have something similar. It would be good to know regardless.