Answer:
A. Bipolar disorder
Explanation:
Bipolar disorder is a brain disorder characterized by massive mood swings that occurs to a person within short period of time.
This will make them act extremely hyper and happy at one moment (such as the roomate when she is saying she is on top of the world) and suddenly revert back to become extremely depressed several days later. Both the swings tend to happen without any justifiable reason.
Currently, there is no cure for bipolar disorder but the patients can take medications to maintain their emotional stability.