When reserving a flight, it is advisable to prepare for possible illnesses or other medical emergencies. Bear in mind that you cannot transfer or cancel your flight due to illness unless you have purchased a special ticket at a higher price.
The best way cover yourself is to take a travel insurance when making the flight reservation. Should you fall ill before the trip and be unable to take the flight, you can seek reimbursement through your insurance policy. When taking the insurance, however, ensure that it does cover cancellations due to illness.