What symptom often signifies the onset of an anxiety disorder?

The symptom that often signifies the onset of an anxiety disorder is excessive worry or fear. This symptom is one of the hallmark manifestations of anxiety disorders, reflecting a persistent and often uncontrolled concern about various aspects of daily life, including health, work, and social interactions.

Individuals experiencing excessive worry typically find it difficult to control their anxiety, which leads to significant distress and impairment in functioning. The anxiety may be disproportionate to the actual situation or potential threat, contributing to a cycle of hyperarousal and avoidance behaviors. This symptom can manifest physically and emotionally, resulting in a range of physical symptoms such as restlessness, fatigue, and muscle tension, further complicating the individual's experience.

In contrast, the other options do not align with the characteristics typically associated with anxiety disorders. Increased concentration and heightened motivation are generally not symptoms of anxiety; in fact, anxiety can often lead to difficulties in focusing and diminished motivation due to the overwhelming nature of the worry. Acute happiness is also not related to anxiety disorders and can be seen as more characteristic of positive emotional states rather than the distress experienced in anxiety. Thus, excessive worry or fear serves as a clear and recognizable indicator of the onset of an anxiety disorder.