An overnight stay at the ICU

Four months ago I did the Executive Health Check and was given a clean bill of health except for the cholesterol which was bordering on the high side. Yesterday I visited the doctor again to check on the cholesterol and see if I needed to take medicine. I was a bit late and was rushing, almost running up the hill to the hospital. On meeting the doctor, as a routine, he checked my heartbeat and found it was beating so, so fast and also irregular. It worried him enough that he held me overnight in the ICU for a series of tests and observation. Thank God, the test showed nothing.
Must be because of the rush.