is he taking any meds or supplements sometimes there is side effects from them.How long has he been like this ?
Oh, one other thought is blood sugar. good luck
Well, obviously the first thing that comes to mind is a heart issue. Also, asthma---- which one does not have to have typical symptoms . . . but he could be low on oxygenated blood. Panic and anxiety can also cause these things.
Is it only when he exerts himself or at resting as well??
Anyway, a doctor is absolutely the BEST place to get your information and am glad you have an appointment soon. Sounds quite necessary and hope you get good news and this is fixable easily. good luck