Hope you're feeling better. Unfortunately, by the letter of the rules, if you didn't cancel the ticket before departure then you forfeit the whole thing. Understandably, canceling the ticket wasn't the first thing on your mind, so you might ask AA whether the residual value of the ticket (total cost minus a change fee) could nonetheless be applied to a new booking. If all this fails, you might make a claim against your credit card's travel insurance policy (if it has one; many higher-end cards do), since this type of situation is covered under many plans.