During the past few years, Lester has experienced several episodes of devastating sadness, weight loss, feelings of worthlessness, and an inability to concentrate. Recently, Lester is experiencing tremendous elation, excessive excitement, racing thoughts, and elevated self-esteem. He has not slept for several days, claiming that he no longer needs a full night's sleep. Which diagnosis will Lester most likely receive from a clinical psychologist?

The diagnosis he is most likely to receive from a clinical psychologist is bipolar disorder.

Explanation:

People who have bipolar disorder present major mood swings. During the state of mania or hypomania, people feel euphoric, elated, or irritable. That can affect their sleep as well as their ability to think clearly. Their behavior is also altered. During the state of depression, people lose interest in activities, and often feel hopeless. Their ability to concentrate decreases, and their behavior is either restless or slowed. As we can see, the symptoms Lester has had fit into the above description. Therefore, the most probable diagnosis for him is bipolar disorder.