I'm 32, female, 5'6", and I'm having an odd feeling in my upper chest, like sets of strong and slow heart beats in my upper chest (from my sternum up) and sometimes even into the throat area... it feels tight when this happens, as if my heart is struggling to beat, or maybe it just feels tight because I'm more aware of it when it happens. But the tightness doesn't feel muscular. This happened a few months ago for several days, I had an ECG and a 24 hour monitor, nothing majorly "off" was found, but I also didn't feel these symptoms when I actually had the monitor on for those 24 hours. I figured it was just stress or anxiety, but I'm off work this week and it started up again even though I'm relaxed. It kind of scares me. I had some headaches the past few days and have been tired in general, but I figured it was just my body catching up from lots of work lately... The only significant thing in my medical history is mono and knee surgery.