Sam Gregory’s flat affect and failure to respond indicate a sudden change in behavior. What could be the diagnosis?

The indication of flat affect and a failure to respond suggests a significant alteration in behavioral functioning, which aligns closely with characteristics seen in catatonia. Catatonia is often marked by a lack of movement and response, alongside unusual or absent emotional expression. The sudden change in behavior, especially when accompanied by conditions such as stupor or rigidity, points towards catatonic features.

In contrast, while schizophrenia can also involve flat affect, it typically encompasses a broader array of symptoms, such as delusions and hallucinations. Major Depressive Disorder might present with flat affect, but it generally includes a spectrum of mood-related symptoms rather than solely a lack of response or movement. Anxiety Disorders usually manifest in heightened arousal and behavioral agitation, which is not consistent with the described flat affect and failure to respond.

Thus, the symptoms of flat affect coupled with the described behavioral change are most consistent with catatonia, making this the most appropriate diagnosis in this context.