Which of the following symptoms is NOT commonly associated with schizophrenia?

Extreme happiness is not commonly associated with schizophrenia and is, in fact, more characteristic of mood disorders, particularly manic episodes in bipolar disorder. Schizophrenia is primarily associated with symptoms that severely disrupt a person's perception of reality.

Hallucinations involve experiencing sensations that are not present, such as hearing voices, which are common in schizophrenia. Delusions are firmly held beliefs that are not based in reality, such as believing one has special powers or is being persecuted, which is also a hallmark of the disorder. Restricted affect refers to a decrease in emotional expression, which is another symptom seen in individuals with schizophrenia, indicating a reduction in their emotional responsiveness.

Thus, while all the other symptoms are central to a diagnosis of schizophrenia, extreme happiness is not typically found within the spectrum of symptoms associated with this mental health condition.