Final answer:
A nurse should immediately perform a rapid assessment of neurological function when a patient's consciousness level changes and quickly communicate the findings to the medical team.
Step-by-step explanation:
When a nurse observes a change in a patient's level of consciousness from alert to lethargic, the best action is to perform a rapid assessment of neurological function. This assessment includes checking reflexes, sensory responses, motor control, and possibly administering the FAST mnemonic (Face, Arms, Speech, Time) if a stroke is suspected. It is crucial because neurological changes can indicate serious conditions like a stroke, requiring immediate treatment to minimize damage to the CNS. Speed of treatment is critical in cases like stroke or TIA, with recovery highly dependent on it. The nurse should communicate these findings promptly to the medical team to facilitate a swift diagnostic process, including a CT scan and interventions such as aspirin therapy to prevent clot formation.