Final answer:
The nurse should move the client with bipolar disorder to a different room.
Step-by-step explanation:
When a client with severe depression reports being kept up by a roommate with bipolar disorder who never sleeps, the nurse should take the action of moving the client with bipolar disorder to a different room. This is because bipolar disorder often involves episodes of mania, during which a person may have racing thoughts, increased energy, and a decreased need for sleep. By moving the client to a different room, the nurse can provide a more conducive environment for both clients to get the necessary rest.