i am a doctor by profession and i would like to provide you some information that i hope you might find useful
firstly: i would like to know that what is the frequency and duration of this suffocation, at rest or during work, nature of pain anywhere?
secondly : what cardiac and lung assessments have you had so far and what was the conclusion by the doctor you consulted
lastly: i would be grateful of you have any recent tests and lab reports that you might like to share so i can shed some light on this matter and if you have a cbc ( complete blood count report) that you could share
one possibility that matches my ability to think on this matter is acid reflux disease commonly known as GERD..acid reflux also leads to symptoms like chest pain and in some population it can give rise to suffocation and heavy feeling like symptoms as the food regurgitates back. it also can result in a gerd related asthma..but i cannot comment unless and until i have a complete clue about the medical history and the symptoms because this post of yours can relate to anything cardiac and respiratory issue as well more importantly.
so i suggest you make an appointment with a good gastroenterologist it might be of great help
hope this helped you a bit and its least likely to be bird flu but like i said cant rule anything out right now