I think you should consider giving your PCP a call and maybe not asking for pred yet (delay it as long as possible) but consider an inhaled steroid burst. For example, if you're on Advair 250/50 consider going to 500/50 for a bit. If you're on Advair 500/50 already, consider adding supplemental flovent 220. Or something to that effect. If you can stave off the oral steroids, it will be much safer for you. Have you been exposed to the flu or pneumonia? What about a cold? Any type of allergy?
For me, sometimes I just get tight. Unexplainable, I know, but that's why I'm intrinsic. Sometimes, I jsut don't find a trigger...