It's been happening quite often lately - I've been feeling breathless for no rhyme or reason, like I have just ran a long distance.

Not sure if it's because I've stopped exercising for quite a while due to my production which I am so busy with. But I think that only explains why I feel breathless easily even when I am simply climbing a flight of stairs, but it worries me when it happens all of a sudden even when I am not doing anything.

Stress? Some hidden physiological condition?

This chart I found online disturbs me... Think I'll go consult a doctor...