Elliptical is completely different from a stationary bike. Bike or cycle is very common to us and all of us experience it at some part of life and is very easily adaptable. Elliptical machine is a complete workout even for your upper body and if you are starting new I would suggest you not to concentrate not on the fat burning or heart rate rather get yourself adapted to the machine. Wear proper shoes, start slow and increase speeds and intensity with comfort. If you still have problems then I would suggest you to do some other type of cardio till you are comfortable. Exercise is something you should enjoy and always go for types of cardio you are comfortable with, swimming, skiing, cycling, running, jogging, skipping, sports etc. anything.
I went back to the bike after having those 2 experiences, never to go on the elliptical again...or at least for awhile. However, on Monday I had the same experience on the bike. I did call my doc and she did see me, but said it was nothing but a migraine which I didn't agree with. I thought given my history it was either Sinus problems or at the most a mini-stroke like my mom had since stroke is very much in our family history. On Wednesday I had two more experiences going into work, 30 minutes apart. I called back to the doc and spent the next 6 hours in ER. I think that was mainly because my blood pressure was going all over the place from 160/52 to 5 hours later 92/38. Heart rate stayed fine between 70 and 80 the whole time I was there. (I've never seen that kind of blood pressure before on me.) So now I've got my answer, I have a sinus infection on that side of my head. I can live with that, no biggie Not that my doc was interested in me asking if I had that when I saw her earlier. She was definite in her answer of a migraine. Any, I'm just glad we found hopeully the root of the problem and it'll be gone.