I don't have asthma but sometimes i feel difficulty taking a deep breath, and sometimes i almost faint, i feel weak and have to sit down. why?

See your doctor: It is time to see your doctor. At 21 Y.O., it is not uncommon to see this situation. Although it may be something more significant, dehydration and a fainting syndrome called autonomic dysfunction should be considered. An ecg, physical examination (including blood pressures while lying down and standing) and an echocardiogram may be indicated.

A few options: Anxiety disorders are common mimics of respiratory symptoms and should be investigated closely. We'd need more information on your situation to provide a more specific list of possibilities. A thorough discussion of how and when these episodes occur would be the key, and this is best done with an in-person doctor visit.

Get checked: You may be hyperventilating causing faintness and weakness. Asthma can cause difficulty breathing. How do you know you do not have asthma?