I wake up in the night with difficulty breathing, but when i run and work out i breath fine. What is wrong?

I had excersise induced asthma as a child, but i took tests recently that said i do not have asthma. I am a varsity track athlete and am in great shape, and in fact my breathing improves when i do excersise. This problem just started to occur very abruptly: one day i was completly normal, the next i was waking up in the middle of the night and having difficulty breathing. Durring the day, i breath fine, but i can feel a small tickle in my lungs when i exhale. These symptoms have been happening for about a week. What the f*&% is going on???