I know I have the same problem.

A couple of times now.... when I am riding really hard and it's really hot/humid... I can get to where I can't get any air in and my throat feels constricted.

It's scary... but I just slow down and try to get my heart rate down.

Yea, I should go to the Doctor and ask about it... but it has only happened twice... and my insurance has a $500 deductible on it before they start kicking in. I'm broke as hell... so I only allowed to go to the Doctor in an emergency situation.