The existence of true unconsciousness is clouded by a seemingly-impenetrable self-reporting problem:

From the perspective of recall, unconsciousness is indistinguishable from a gap in memory.

There is no way for a person to determine whether they were truly unconscious or just conscious at a sub-memory level.

(This is why I personally doubt the existence of true unconsciousness. I think it’s entirely possible that consciousness is uninterruptible, at least during the lifetime of a conscious organism.)