Thanks- yeah, it just feels like when you can't get a knuckle to crack, only it's your lungs - like you're trying to yawn and it won't work. I'll check out the Magnesium thing, although recent bloodwork for a virus, and then followup didn't turn up any magnesium abnormalities. I know sodium and phosphorous were way off at first, but returned to normal. In any case it's a good idea to take calcium and magnesium after working out, so I've reinstituted that protocol. Thanks for the suggestion!