when you say stim - would that include coffee/caffiene?
All stims can cause blood vessel constriction and depending upon how severe it is and where it is, this can lead to decreased circulation of oxygen because bloodflow is reduced. Some people who have asthma (who may not even know they have asthma) will sometimes have asthmatic reactions caused by stims. Then there are allergic reactions which can always happen.
He said that this started happening when he started taking two substances:
Epistaine
Dialene 4
I guessed the stim was the culprit because it would be very unusual for a steroid to cause blood vessel constriction, decreased red blood cell count, or allerigic reaction.
On the other hand, Dialene 4 is an exotic blend of stims. Wouldn't suprise me a bit if the stim caused certain people to have allergic reactions, asthmatic trigger or blood vessel constriction.
I only chimed in because people don't take yawning seriously but IMHO any symptom that COULD be a result of lung or cardiac malfunction should always be taken seriously because of the potential for sudden death. Most of the time you'll be overreacting but you don't want to be the guy at the gym who drops dead because he ignored that shortness of breath which nagged him for a week.