Chronic fatigue syndrome tends to arise suddenly in otherwise active individuals. In a typical disease course, an otherwise ordinary flu-like illness or some other stressor will leave behind unbearable exhaustion and symptoms of CFS. This condition is frequently mistaken for a recurrence of the infection, sending the patient back to the doctor for more tests. Repeated tests will reveal no characteristic abnormalities, yet symptoms worsen, eventually resulting in sleep disturbances and depression. Many patients with CFS feel their concerns are initially dismissed by physicians, friends, and family, which may contribute to a sense of isolation. Once diagnosed, the symptoms may fluctuate, but CFS is not a progressive disease. Instead, most patients tend to get better by degrees, and some will fully recover.