Looking for Advice on Exercising with Hyperadrenergic POTS

I just started going to the gym, and by just I mean I went one time so far lol. They have a semi-recumbent bike. I felt like I could definitely handle it. My heart rate was around 120-130 on it. After that I went on the elliptical (I knew it was kind of a bad idea, but I was feeling daring) I did nine minutes and my HR gradually went up to 187. I felt like crap for a few hours after that like all the blood drained out of my head.. Id say just take it slow and don't over do it. Work your way up to harder exercises as they say. Short walks are good as well, I walk my dog most days for about 10 minutes and I think it helps me. Also I feel for you, its been kicking my butt too lately.