actually, since you are doing your classes online it might be a nice thing to help keep you busy while you are recovering and just think, while you are reaching one goal of losing weight and getting healthier, you are also feeding your head with an education! two birds with one stone! you should be proud of yourself, i'm sure you will do great!
and if things are too overwhelming, like others have said, i'm sure the school would understand if you needed to withdraw if you explain to them ahead of time all about your situation.
good luck!