Almost passing out after work outs

I've been having some weird symptoms lately and I'm hoping someone here will have some advice for me. I started going to the gym 1 month ago and everything was going fine. I was using the elliptical for 30-45 minutes a day, 3-4 times a week. 3 weeks ago I went to the gym and 11 minutes into my work out I started feeling dizzy, like I was going to pass out. I left and went home. I have anxiety and panic attacks so I assumed that's what it was. When I got home I decided to resume my work out on our treadmill, which I did for 22 minutes. A few minutes later I had the same feeling I had at the gym, like I was going to pass out. When I use the elliptical I normally go a speed of around 5 and on the treadmill I was at a speed of 4.7 on a 9-10 incline, so it's not like I was working out really hard. I was drinking water throughout the workout and I had consumed 1,110 calories that day prior to my work out, however the last time I had eaten was 4 hours before I went to the gym.

After this incident I took a break from the gym for a couple weeks because of what happened. I thought a medication I was taking (pantoprazole) for a hiatal hernia/acid reflux had caused the fainting feeling. I was taking this medication when I first started working out (and felt fine) but was told to double up and went from 40mg to 80mg daily, which is when I started having these fainting problems. I switched to a different medication (only 40mg daily) and decided to try the treadmill a couple days ago. I was fine throughout the entire workout (30 min) until afterwards. A few minutes after I finished I started getting heart palpitations (I'm talking 6-7 in a row. I've been having palpitations for a few years but usually only 1 at a time. The most I get are 2-3 in a row. I always blamed my birth control because I never had them before I started taking it. ) and I got the same fainting feeling as before. Now I'm scared to death to work out. This time I was only going a speed of 4 on the treadmill and I had consumed 950 calories prior to the work out.

I just can't understand why this is happening to me. I used to work out a few years ago and never had any problems. If anything my diet is better than it used to be so I should be healthier. I thought my medication was causing low magnesium (which is one of the side effects, although it's rare) but my doctor didn't think so. He said that it can cause dizziness and make you feel lightheaded but he didn't say one way or another if he thought the fainting feeling was related to the medication. I have an appointment with a cardiologist at the end of the month because I really need to find out what is causing those palpitations. I was serious about getting a bikini body this year and this is what happened Has anyone else experienced anything like this before? Any suggestions as to what it might be?