Thanks for your answer!
With his mild form of asthma, I expected him to struggle quite a bit, but apparently he dealt well with the conditions so far. That surely must have given him a bit of confidence, even if he hasn't yet been tested (the same fact goes for Roger and Rafa btw).
I'm no expert, nor esp informed poster, but as I understood from more knowlegable people and some interviews (mainly that of his and Rafas PR
man Barbarilo), Nole has a classic case of undeveloped thorax (the part of the human body between the neck and the diaphragm, partially encased by the ribs and containing the heart and lungs; the chest) due to nose deviation that he operated on couple of years ago - his lungs couldn't develop properly when they were due.
Such condition, while common and not esp hard on ordinary people can greatly affect professional athletes who travel the world and are exposed to various climate conditions.
That coupled with immunity problems (that are kinda side effects to this small thorax thing), competitive frustrations and anxious moments in crunch time, can lead to severe falls of play, best seen at Monte Carlo when he retired against Roger.
I believe that he is a smart young man, and is surrounded with smart people (barring some exceptions) that advise him to take it easy. So I think that the best of him in competitive and trophy terms is not to be seen until some years in the future, when his medical condition is brought in proper order. Until that time, however, breakdowns of that stamina/anxiousness type will still exist.