Woke up unable to breath. I felt like my chest would go inwards. Ventolin helped. Got cough/yellow mucus. Normal xray. This can only be asthma right?

Other possibilities. Other possibilities for your symptoms would include gerd, post-nasal drip or a combination of these, including bronchospasm. You should see your doctor asap to be sure your symptoms are due to bronchospasm and to rule out any other diagnosis. All these have different treatments. You should also be on a steroid inhaler to decrease inflammation. And, if you smoke, you need to quit. See your doctor!
No. Asthma isn't the only thing that can cause your symptoms. Ventolin acts to relax the smooth muscle surrounding the airways, thus dilating them and making it easier to breathe when airways are constricted, but asthma is not the only thing that causes such airway constriction.