Which of the following is a physiological sign of someone struggling?

Rapid breathing is a physiological sign of someone struggling because it often indicates a state of stress or anxiety. When a person is in distress or facing a challenging situation, their body reacts by entering a "fight or flight" response, which can lead to an increase in heart rate and respiration. This change in breathing pattern is the body’s way of ensuring that it gets more oxygen to fuel the muscles and prepare for potential action or to cope with the situation at hand.

In contrast, the other options suggest more stable or positive physiological states. An increased appetite, regular sleep patterns, and a calm demeanor typically indicate that a person is not experiencing immediate distress or struggle. These signs suggest well-being and balance, rather than the heightened state of alertness or anxiety associated with rapid breathing.