Hello Sarah:
First, sorry it took me so long to get back to you here. We were having problems with MSN and couldn't post for a few days. Actually, almost all questions I get from the AskJoel board are via direct email. It is the best way to get the quickest responses for I get those emails almost immediately and don't have to deal with posting problems that we encounter from time to time during MSN upgrades.
As to why your lungs may be hurting, I am going to attach links to a few video that discuss this issue. It actually addersses your other question too. I am going to attach links to a few articles that also address issues that your questions pose. Hope this helps answers your concerns.
Joel
Articles: