A person is excused from fasting if they have a condition that is likely to injure their body, make them sicker, or cause them to recover more slowly. A medical expert should be consulted to establish the extent of the disease. People who have a slight cough or fever should still fast because it usually won't do any harm. When determining whether or not you are too sick to fast, keep in mind that fasting, even when healthy, involves some discomfort.