According to WebMD, atypical depression is a type of depression or dysthymia that involves different symptoms than standard depression or dysthymia. One primary difference between atypical depression and classical depression is a patient's mood reactivity. Patients suffering from atypical depression experience emotional reactions to positive and negative life events, whereas patients suffering from typical depression are generally not emotionally responsive to external events.
Mayo Clinic states that common symptoms of atypical depression include hypersomnia, weakness of the arms and legs, difficulty maintaining relationships, overeating and weight gain. Some primary differences between typical and atypical depression are sleeping patterns and mood reactivity. In classic, or melancholic, depression, difficulty sleeping is more common, whereas in atypical depression oversleeping and fatigue are more common. Patients suffering from any type of depression may feel sad, guilty, hopeless or worthless.
Psychiatric Times explains that in patients suffering from atypical depression, positive life events can change this mood, if only temporarily. Patients suffering from atypical depression are able to feel 50 percent better, and possibly even euthymic, in response to positive events. As long as positive events are ongoing in the patient's life, the elevated mood may remain for an extended period of time. Atypical depression patients' rejection of sensitivity appears to be a constant trait, more severely present during depressive episodes.