The inability to stay awake and alert during the day, resulting in periods of an irrepressible need for sleep or unintended lapses into drowsiness or sleep. Excessive daytime sleepiness is the cardinal symptom of narcolepsy.1 Patients may report manifestations such as tiredness, fatigue, drowsiness, difficulty concentrating, or mood changes rather than excessive daytime sleepiness specifically.8-10 Narcolepsy should be considered in all patients reporting manifestations of this symptom.7,11