I have the same problem, I also have problems with high blood pressure, low potassium, vitamin B and well a few other things, plus I have hyperhydrosis and well, the list is longer then my dick.
But anyway, the thing is, it depends, it could be a lack of cardiovascular conditioning, it could be asthma (which I got too), it could be dehydration, it could be fatigue, well it could be anything.
For me it's probably a combination of things, my doctor tells me to pull back a little bit, but I don't, I'm medically cleared and I'm looking after my self in every which way I can.
Go to your doctor, have him check you over, ensure everything is fine and if you've got no problems then start ruling things out, ie, drinking more water first for a few weeks if that works for one symptom try increasing your cardiovascular conditioning and so on and for forth.
But only do that after you've had medical clearance to do so!