Carleen comes to therapy because she is feeling sad. carleen says she has often had periods of extreme sadness in the past and they typically last between 6 and 8 months. during those times she overeats, has trouble sleeping, feels exhausted all the time, and thinks a lot about dying. at other times, however, carleen says she feels wonderful. during those times, which last about a week, she gets a lot done, feels as if she could do anything, talks a lot and quickly, and doesn't sleep but doesn't feel tired. carleen says her "up" times are great and have never caused her any trouble. carleen's most likely diagnosis is