What signifies a decreased level of alertness in a patient?

A decreased level of alertness in a patient is indicated by a Glasgow Coma Scale (GCS) score of less than 15. The GCS is a scale used to assess a person's level of consciousness, primarily following a head injury. A score of 15 suggests that the patient is fully alert and responsive, while any score below this indicates varying degrees of impaired consciousness. For example, a score of 13-14 may suggest mild impairment, whereas lower scores indicate more significant levels of decreased responsiveness.

In contrast, the other options—such as normal responses to external stimuli, full comprehension of questions, and the ability to recall past events—demonstrate that the patient is functioning adequately in terms of alertness and cognitive abilities. Therefore, these options would not signify a decreased level of alertness.