Excessive daytime sleepiness is a symptom that can make it difficult to stay awake during daily activities. It may be associated with narcolepsy, obstructive sleep apnea, shift work sleep disorder, or other health concerns. Modafinil may be prescribed for sleepiness linked to certain diagnosed conditions in adults. Finding the underlying cause is important because treatment depends on the person's specific situation. Anyone experiencing persistent daytime sleepiness should seek medical assessment rather than self-medicate.