How do grad schools look upon students with chronic illnesses?
Do any of your letter writers know about your illness and can speak to your strength in spite of it? If your application on its face is strong (ignoring the withdrawn course and year gap), a mention of your illness and overcoming it in your personal statement (not your statement of purpose!) might be a good thing to do. I do not think they will look down upon you for this, quite the opposite. From what I have read, they cannot discriminate against you simply based upon your illness so that shouldn't be a problem (see ADA). If it's clear that you're dedicated, I think you'll be okay.