Your roommate is acting very strangely. Although she has not slept much in the past few days, she says she is on top of the world. She has cleaned and re-cleaned her closets several times. She has invested in a questionable financial venture. This period of non-stop activity has lasted for well over a week and is in sharp contrast to the depression and fatigue she exhibited in the previous semester. The DSM-IV diagnosis would most likely be

Bipolar disorder

Explanation:

Bipolar disorder is characterised by periods of mania followed by a period of depression.

In manic episodes:

Inflated self-esteem or grandiosity

Decreased need for sleep

Increased talkativeness

Racing thoughts

Distracted easily

Increase in goal-directed activity or psychomotor agitation

Engaging in activities that hold the potential for painful consequences, e.g., unrestrained buying sprees

In depressive episodes:

Depressed mood most of the day, nearly every day

Loss of interest or pleasure in all, or almost all, activities

Significant weight loss or decrease or increase in appetite

Engaging in purposeless movements, such as pacing the room

Fatigue or loss of energy

Feelings of worthlessness or guilt

Diminished ability to think or concentrate, or indecisiveness

Recurrent thoughts of death, recurrent s*icidal ideation without a specific plan, or a s*icide attempt