Suffocating in my sleep?- PLEASE ANSWER?

Every once in a while, I will be dreaming and all of the sudden i just won't be able to breath. It feels like a major asthma attack where no air gets in at all. It's the most terrifying feeling i've ever had!!! This just started a few months ago, and it seems to coincide with when I was diagnosed with asthma, and given inhalers. Ever since started using the daily one, my asthma has gotten worse, including in my sleep. Has this ever happened to anyone else? How can i stop it? I sleep with my rescue inhaler under my pillow because I'm so scared that I will wake up and not be able to breathe. That hasn't happened yet, but I'm afraid that i might eventually happen.