Final answer:
The nurse should assess the client's emotional state with empathy, offer supportive counseling, and consider referring them to a mental health professional.
Step-by-step explanation:
When a nurse observes a client exhibiting rapid shifts in emotion—from laughing and joking to crying about a death in the family and then quickly back to laughter—the nurse should consider the emotional and psychological state of the client. The nurse needs to approach the situation with empathy and provide support. An appropriate course of action might involve gently engaging with the client to assess their mental health, offering supportive counseling, or referring the client to a mental health professional if the behavior suggests an underlying psychological issue such as mood swings or a grief reaction.