If you keep worrying, you will be stuck in a vicious cycle of worry, generating more anxiety, precipitating more symptoms, which will further increase your worry. The tests you have done are very much reassuring. If still in doubt regarding asthma (if you have risk factors such as a background of respiratory allergy, a 1st degree relative with asthma), then have yourself evaluated for that. Otherwise, you need to resort to the techniques I have previously mentioned to fight stress and abort the worry-anxiety symptoms-worry cycle.