I have difficulty breathing comes suddenly last for 1-2 hours, sometimes disappear for a period and come back make me sigh a loty my ecg excellent.

Normal heart: Without examining you, it's impossible to say what is going on in your case. However, a normal ecg does make it more likely that the symptoms are caused by anxiety or stress. However, blood clots to the lung are also able to cause such symptoms. If you smoke, take birth control pills, or have had long periods of immobility (or airplane travel), see your doctor.