diagnosis

via wikipedia:

excessive daytime sleepiness (EDS) is characterized by persistent sleepiness, and often a general lack of energy, even after apparently adequate night time sleep. Sudden involuntary sleep onset, and microsleeps are common complications. EDS is one of the two forms of hypersomnia, the other being prolonged nighttime sleep.

Some persons with EDS are compelled to nap repeatedly during the day; fighting off increasingly strong urges to sleep during inappropriate times such as while driving, while at work, during a meal, or in conversations. As the compulsion to sleep intensifies, the ability to competently complete tasks sharply diminishes, often mimicking the appearance of intoxication.