What do you think causes the feeling in young children of not being able to breathe?

Because google couldn't give me a good response, I came here. I myself suffered from feeling like I couldn't breathe as a child, and was diagnosed with asthma. Looking back, I don't think I ever had asthma. I would sit there in the guidance office with a nebulizer and know that I didn't need to use it. Looking back, I think that it was all just psychological. I could go off on a rant about how doctors just want to give a simple diagnosis and move on with their lives instead of trying to find a root problem but I won't. The thing is, I've always had anxiety. But at that age, I didn't even know what anxiety was. I didn't have much to be stressed about. My little brother is now saying that he can't breathe a lot(he's seven) and I can more than relate. It's just that when you ask him about it he's very vague as many seven year olds are. I'm just wondering in your personal opinion, what do you think causes the feeling in a young or developing child of not being able to breathe...other than physical conditions such as asthma or other respiratory illnesses?