Can't really say what is causing it, could be important or could be nothing but you should go and see a doctor and get checked out. Just try to describe as much as you can about what happens, what you feel and when it happens. Best of luck sorting it out.
It sounds like a classic panic attack. I would suggest you google this:
Symptoms panic attack
If what you read does not describe anything you experience, then see a general practitioner for an evaluation.