an exclusion criterion on depression and depressive disorders is past history of a 'mixed state'. a 'mixed state' is the presence of mania or hypomania. if there is a past history of mania or hypomania then you don't get a dx of depression (which is a uni-polar disorder - depression with no mania / hypomania) instead you get a dx of bi-polar or bi-polar II depending on the extent of the manic.

there is some controversy over bi-polar II. a way of turning an axis II into an axis I methinks ;-)