Is This Really Asthma?

Is it possible to have an asthma attack--chest tightening and difficulty breathing--without a cough or wheezing. I rarely have a cough (not even in the mornings) and, therefore, there is never any phlegm. I had an EKG, and was told that I'm not having a heart attack, and my chest x-ray was clear. My breathing difficulties are worse at night.