After my longest run ever on Sunday (2 and 1/2 hrs) I noticed my heartbeat had become irreguar. I had it checked out at the hospital and was told it was caused by the large amount of adrenalin in my system, and to take it easy and the symptoms should disapper - I had some tests to make sure it wasn't life threatening. I am supposed to be doing the Great North Run on Sunday - and am not sure whether to go for it or not!! Any advise welcome!!!