Uh Oh!

Today was day 3 in a row of no panic attacks.  Worked from home.  Busy but otherwise not bad.  Stomach is so so.  Calories are low.  Gotta find some things to eat that are healthy.  Figured I would go to the Y tonight.  Got on the treadmill and it felt ok.  Did 5 minute warm up, feeling pretty good.  Then I did 3 1/2 minute jog, 4.7 mph.  Got my heart rate up to 174, starting feeling whoozy and slowed down to 3.7 mph walk.  got my heart rate down to 144 bpm.  Walked for about 3 1/2 minutes, then jogged again, 3 1/2 minutes.  still ok then walked.  Then jogged for 3 minutes.  this jog got scary.  I started getting dizzy and did heart rate and it was at 184.  So I slowed down to 3.7 mph and got heart rate down to 154 bpm.  figured I would just walk the rest.  Usually, I get my heart rate down in low 140's.  But it was not going down.  At least according to the treadmill's heart rate monitor.  so I walked the rest of the time, 36 minutes total.  At 29 minutes I began slowing down and got all the way down to 2.4 mph but heart rate still seemed a little high. 
I decided against doing the weights.  I figured I better get home.  A little light headed in car.  Sitting here now trying to calm myself down.  Doesn't really feel like a panic attack but not 100%.  I just had a stress test not too long ago and ultrasound on carotid artery and something else on my heart as well as ekg and all ok.  so just wondering if I got myself worked up too much too fast.  I did have some really fast beat music going. 
Anyone else out there have this happen to them?  Scared me a little.  Never happened before.  Don't want to take Xanax if I don't have to.