Which term refers to a difficulty in initiating or maintaining sleep?

The term that describes a difficulty in initiating or maintaining sleep is insomnia. Insomnia is characterized by persistent problems falling asleep, staying asleep, or waking up too early and not being able to go back to sleep. This condition can lead to significant impairment in daytime functioning and may be caused by various factors, including stress, anxiety, depression, or certain medical conditions.

In contrast, sleep apnea is a disorder involving interrupted breathing during sleep, which can lead to significant fatigue and other health problems but does not specifically refer to difficulty in initiating or maintaining sleep. Narcolepsy is characterized by excessive daytime sleepiness and sudden sleep attacks, while cataplexy involves sudden loss of muscle tone typically triggered by strong emotions, rather than issues with sleep initiation or maintenance.