Need help with health consequences of belly inflation

Hi! This question goes out to anyone who knows medicine/health in the community.

I recently ran into a problem. I don't use a pump for inflation. I simply eat and drink. And most importantly, I use a sort of 'Valsava manueve' or breathing technique to push/breathe air into my abdomen from my lungs or from the outside to enlarge my belly.

I've been doing this for years without consequences. Although sometimes, my heart starts racing, but eventually returns back to normal.

But two months ago, my heart started racing and pounding nonstop for two days. For two months I've been experiencing symptoms like giddiness, numbness, fast resting heart rate etc.

I've visited the doctor but passed everything (chest xray, echocardiogrram, ecg, blood test) all with negative results. They couldn't figure out what was wrong with me.

any ideas what happened? Any help from the community s much appreciated :)