Complex sentence: An adult who is compelled to nap repeatedly during the day may have excessive daytime sleepiness; however, it is important to distinguish between occasional daytime sleepiness and excessive daytime sleepiness, which is chronic.
Split into simpler sentences: An adult who is compelled to nap repeatedly during the day may have excessive daytime sleepiness. However, it is important to distinguish between occasional daytime sleepiness and excessive daytime sleepiness, which is chronic.