Final answer:
Nicholas is most likely experiencing insomnia, a sleep disorder characterized by difficulties in falling asleep and remaining asleep, along with complaints of non-restorative sleep and daytime fatigue.
Step-by-step explanation:
The sleep disorder that Nicholas is most likely experiencing is insomnia. Insomnia is characterized by difficulties in falling asleep and remaining asleep, along with complaints of non-restorative sleep and daytime fatigue. Individuals with insomnia may have long delays in falling asleep, wake up several times during the night, and find it difficult to get back to sleep. Insomnia is the most common sleep disorder, affecting a significant portion of the population.
Insomnia requires experiencing these difficulties for at least three nights a week for at least one month's time, according to Roth (2007). While there are various sleep disorders, such as sleep apnea and narcolepsy, which have other distinctive symptoms, the description given best fits the criteria for insomnia.