Chronic Fatigue Syndrome
Also, it should be noted that depression actually is a physical illness. The overlap in symptoms between depressiona and chronic fatigue syndrome is likely due to common mechanisms involving brain chemistry, including abnormal levels of the neurotransmitters serotonin and dopamine. Many people with chronic fatigue syndrome become depressed, but that's generally believed to be the result of living with a debilitating illness. People with other serious illnesses, such as cancer, also are at a high risk of depression.