Is parasomnia a catch-all for sleep disorders otherwise not explained?

No: Parasomnia refers to a sleep disorder that results in people engaging in certain behaviors while their brains are almost entirely still sleeping. Sleep walking and sleep talking are examples. Some parasomnias occur during deep sleep and some during REM sleep. They usually occur in childhood and dissipate. Some adults however develop parasomnias and this may warrant a sleep consultation.

Oh no!!: Parasomnia is only a fancy expression for sleep problems that do not cause daytime sleepiness, that are not sleep apnea, insomnia or circadian rhythm issues. Parasomnia have a wide range and include nightmare, sleep terrors, sleep walking, sleep eating, sleep sex, snoring, rem behavior abnormalities and more.

Parasomnia: Parasomnia refers to things during sleep where something is going wrong, such as movement, night terrors etc, as opposed to insomnia where there is a problem falling asleep staying asleep or both. Yes it is a broad term that includes a lot. So it wouldn't be someone's actual diagnosis, the diagnosis would be more specific.