Question: If I have a medical condition, or have recently had an operation, can I still fly?
Answe: Maybe. It is your duty to inform us of any medical condition you are having at the time of travel. This can be done by contacting our Call Centre.
We recommend you to discuss your journey with your doctor prior to making a reservation, or furnish us a medical clearance issued by the relevant authorities. In any event, we reserve the right to refuse carriage if we deem you unfit for travel. – source: AirAsia FAQ