Manic-depressive psychosis is a severe disturbance of affect (feeling or emotion) characterized by extreme and pathological elation such as extreme excitability, volubility and foolhardiness, sometimes leading to physical exhaustion, alternating with severe dejection or depression; both of which may last for months or years. There may be normal intervals between these states, and cases are known in which only the manic or the depressive attack occurs once or repeatedly. Attacks usually alternate with intervals of complete health.
Due to the unpredictable nature of manic-depressives, it is impossible to rely on them for responsible action and judgement. While they may be very alert and mentally capable during their manic phase, they can experience extreme feelings of guilt and unworthiness and even lean toward suicidal tendencies in their depressive modes. As manic-depressive psychosis is not immediately recognizable, unknowing persons may get involved in the patient's manic schemes, only to be disappointed when the intended outcomes never materialize.