For the last 2 hours, I have felt a noticeably throbbing just under my collarbone, on the left side (below my neck). Is this serious enough that I should consider going to an emergency room? Or could this wait until morning, when I d call my general physician about this & make an appointment? I m concerned. Other information - I m a white male, 61 years old. I have a slight arrhymia for which I take 25 MG Atenolol each day. I m in generally good health, though overweight by 15 lbs (height- 5 4 ). What do you think of this? Serious? Or could it (perhaps) wait until morning?