The most likely diagnosis is generalized anxiety disorder (GAD). The DSM-5 diagnostic criteria for GAD are as follows: 1) excessive anxiety or worry about a number of events or activities (for example, school or work) occurring more days than not for at least 6 months; 2) the patient recognizes it is difficult to control the worry; 3) the anxiety or worry is associated with at least three of the following symptoms: restlessness, easy fatigability, difficulty concentrating, irritability, muscle tension, and sleep disturbance; 4) the anxiety, worry, or symptoms cause impairment at school, work, or other settings and cannot be attributable to medical or other psychiatric conditions, medications, or substance use. A useful tool for identifying and assessing the severity of GAD is the Generalized Anxiety Disorder 7 (GAD-7) assessment tool that rates seven items on a scale of 0 to 3 based on increasing severity. A score of 5 to 9 indicates mild anxiety, 10 to 14 moderate anxiety, and 15 to 21 severe anxiety. This patient meets the DSM-5 criteria, and his GAD-7 score of 13 is consistent with this diagnosis. Treatment options include psychotherapy and medications. Cognitive-behavioral therapy is the most effective psychotherapy for GAD and in trials has been shown to be as effective as medications.

Symptoms of GAD overlap with those of attention-deficit/hyperactivity disorder. However, the main symptoms that this patient is experiencing are worry and anxiety with associated physical symptoms.

Patients with GAD may manifest symptoms of depression; indeed, patients with anxiety disorders may also experience depression. However, the main symptoms that this patient is experiencing are not related to mood, but rather to worry and anxiety.

This patient is not manifesting symptoms of obsessive-compulsive disorder (such as recurrent and persistent thoughts or impulses), making this diagnosis unlikely.