A person owes many missed fasts and prayers from a time when he was healthy, but is now... - Jurisprudential Answers - Book of Fasting

Ahmed al-Hasan Response:

A sick person who owes make-up prayers and fasts from days when he was healthy should wait if he hopes to recover, then make them up and offer the required expiation. If his expiation is by feeding poor people, he must begin feeding them even before recovery. If his illness is chronic and he cannot fast, he pays the prescribed fidya of 3/4 kilogram of food for each day.