Short breathed when laughing

Hi,

I have in the last few months the feeling that I’m short breathed especially when i laugh. I had Thorax CT and the doctors didn’t find anything. I had ultrasound for my neck and throat and also they didn’t find anything, the doctors say they cannot find anything that is unusual, they say everything is totally alright.

I smoke, about 10 cigarettes a day, but i don’t know can it be from that.

What could it be? I worry that it might be some cancer, but then on the other end the doctors didn’t find anything.

What do you guys think it could be?