In certain cases, absence of the gag reflex and pharyngeal sensation can be a symptom of a number of severe medical conditions, such as damage to the glossopharyngeal nerve, the vagus nerve, or brain death.
At one point, it was thought that a lack of the gag reflex in stroke patients was a good predictor for dysphagia (difficulty with swallowing) or laryngeal aspiration (food or drink entering the larynx), and was therefore commonly checked for.