The reason for Carrie's symptoms is "stress".
Stress is a physical, mental, or emotional factor that causes tension to the body or the mind of an individual. Stresses can be external or internal. If they are external, the source of stress comes from the individual's environment. If it is internal it is probably due to illness or a medical procedure.
Stress leads to a gradual deterioration of an individuals well-being, as constant tension will eventually have negative effects on the body.