Which statement best distinguishes primary insomnia from hypersomnolence disorders?

• A. Hypersomnolence disorders involve excessive daytime sleepiness despite adequate nocturnal sleep.
• B. Primary insomnia is difficulty initiating/maintaining sleep with daytime impairment.
• C. Primary insomnia includes excessive daytime sleepiness.
• D. Hypersomnolence disorders are defined by difficulty staying asleep at night.

Answer: (B)

Understanding the difference between insomnia and hypersomnolence hinges on what is driving the problem: trouble with sleep itself versus sleepiness during the day despite enough night sleep.

The best statement captures that primary insomnia is defined by difficulty initiating or maintaining sleep, with daytime impairment. This combines the night-time sleep disturbance with the daytime impact, which is the hallmark that sets insomnia apart from hypersomnolence. Hypersomnolence disorders, on the other hand, are defined by excessive daytime sleepiness despite adequate or normal nighttime sleep, not by trouble falling or staying asleep.

The other options describe aspects of hypersomnolence or misstate the features of insomnia. For example, hypersomnolence is characterized by daytime sleepiness, not by difficulty staying asleep at night; and excessive daytime sleepiness is not a defining feature of primary insomnia.