Do you burp a lot when that happens? (most likely GERD then)
And ALSO, allergies or stuffed sinuses can cause that. If I have a cold or stuffy sinuses and run up the basement steps I feel horrible! Heart pounding, shortness of breath, shaky, etc. (normally I can run up and down 10 times and nothing happens) so sinus issues TOO can cause it, I forgot to mention that the first time, but rereading the posts I saw patmob's post and it reminded me.