The depressive phase of bipolar disorders has some features that distinguish it from unipolar endogenous depression on the one hand and reactive or situational depression on the other hand. The depressive phase of manic–depressive disorder is often accompanied by apathy predominating over sadness, psychomotor inhibition over anxiety, and hypersomnia over insomnia.
Another difference described in the literature on bipolar and unipolar depressions is that, in the former, there is less anorexia and weight loss while emotional lability and the probability of developing psychotic symptoms in severe cases are greater. Epidemiologically, the age at which the disorder begins, in bipolar depression sufferers is younger and the incidence of postpartum episodes is greater.Other differences characteristic of bipolar forms are a family history of mania and completed suicide, and good response to lithium (Dunner, 1980). In young patients, the presence of catatonic stupor is frequent, and in the elderly, pseudodementia is likewise frequent.