So my boyfriend and I got gym memberships and we had our first workout today. It actually went pretty well, it feels pretty good to finally start this. However...

I have a fast heart rate. I have for a while, and I think it's mostly why I lost my job. I was missing lots of work days because an hour or two into my shift id get extremely nauseous and dizzy and have to leave. I eventually got laid off. It's been nearly three months and I've heard nothing back from them.

When I worked out today, my heart rate was all the way up to 150 bpm. Is that dangerous?? Like could I die from that? Or will it eventually help me (since active people tend to have lower heartbeats)? It's kind of scary. All I was doing was fast walking, it wasn't anything too crazy. 

My bpm usually rests at 90-110 resting. And went up to ~150 when I was walking fast for around 20min

Just looking for some advice. I'm trying to get in contact with my doctor currently also.