Originally Posted by Darkland

Could be a number of factors but regardles I would talk to your doctor.

That being said, take a look at how you are breathing during these exercises. From your description it sounds like you get these symptoms with high exertion exercises.

You would be surpised at how many people don't even think about their breathing and hold it while exerting themselves depriving their muscles with much need oxygen. This causes light headedness, increased heartrate, etc.