Final answer:
The client's rapidly beating heart and shaking hands in response to an approaching diagnostic test is an example of the fight-or-flight response.
Step-by-step explanation:
The client's rapidly beating heart and shaking hands in response to an approaching diagnostic test is an example of the fight-or-flight response. This response is a physiological reaction to a perceived threat or danger, preparing the body for physical activity to either fight or flee. The sympathetic division of the autonomic nervous system is activated, resulting in increased heart rate and other defensive/offensive behaviors.