Final answer:
The symptoms described are consistent with bipolar disorder, characterized by alternating periods of manic behavior and depression. This is the most likely diagnosis provided by the DSM for the roommate's described behavior, contrasting with signs of other disorders such as borderline personality disorder or dysthymia.
Step-by-step explanation:
The case described suggests a mental health condition characterized by periods of heightened energy, little need for sleep, and risky decision-making, followed by bouts of depression. This pattern aligns with bipolar disorder, which is known for such manic and depressive episodes. Given the behaviors of cleaning and reorganizing closets multiple times, investing all savings in a risky venture, and the stark contrast to previous depressive symptoms, bipolar disorder seems to be the most likely diagnosis.
It's important to note that while signs may point to bipolar disorder, only a qualified health professional can make an accurate diagnosis after thorough assessment. Personality disorders, such as borderline personality disorder, typically manifest differently, with more of a focus on interpersonal relationships and self-image. Dysthymia (persistent depressive disorder) and depressive mania are not consistent with the symptoms of high energy and risk-taking described in the question. Therefore, according to the DSM (Diagnostic and Statistical Manual of Mental Disorders), the correct answer would be c. bipolar disorder.