Leaving the Gym Early

I went into tonight's workout with high hopes.  Early today I felt great, and was looking forward to using that momentum to get a long(ish) run (like 4 or 5 miles) as well as do a little arm work.  Unfortunately, things did not work out as planned.

I started out enthusiastic, got in a quick warm-up on the elliptical and even did my first few arm stations without issue.

It was when I hit the treadmill that things went wrong.  My first mile went by pretty quickly, especially as I was silently "racing" the guy next to me the whole time (gotta do something to keep yourself busy).  Once I started into my second mile I started getting sharp pains in my side.  I figured it was just a gramp, started breathing deeper and kept pushing on.  By 2 1/2 miles I was ready to throw up.  Regrettably I ended up stopping early and heading home.  Even now, I still feel like I'm going to throw up, and I'm not sure why.  Hopefully I can get to the bottom of it by tomorrow.