happens to me all the time. it's probably exercised induced athsma, though i would have it checked out anyway. drink lots of fluids and humidify your air. there are drugs that help with the bronchospasms, but check with your doctor before you use em - they're a stimulant and don't combine well with things that affect heart function, eg. thyroid meds.

an air filter for your sleeping space might be a good investment as well.