I think I spoke too soon

I thought I was going to make it through these holidays injury-free. I hoped, I even blogged about it.
I wasn't quite so lucky.
Sunday, I was scheduled to work from noon until 5, and my boss asked me to stay until 8 to close the department.
Around 4 pm, I was unloading stock in a cooler (I work in a grocery store), came out and went to page the store manager, and felt a sharp stabbing pain my my left chest area. It was hard to breathe, and I couldn't quite see straight.
I sat down on the counter for a bit, trying to relax and take a few deep breaths. That hurt even more. I tried to wait it out, but the pain just got worse.
I eventually called the manager over, saying I needed to go home or something.
I took a cab to the hospital, and waited in emergency for about 3 hours. When I finally saw the doctor, he diagnosed me with what I assumed I had: a pulled/sprained muscle in my chest wall. He suggested just Advil, and ice, and to take it easy. I haven't been able to knit much, which has just made everything boring. I am used to sitting around and knitting, and this whole not doing anything with my hands is an entirely foreign feeling.
It has started to feel better, which is nice. Still not 100%, but I didn't expect to bounce right back.
All this to say, better safe than sorry. Because it was the left side of my chest, and the recent occurence of heart problems among some of my parents friends, I didn't want to take a chance.