Anonymous“doubtful to you that the past participle form of intransitive nouns like "vanish" and "sleep" could function as adjectives?”
Just as an aside, we should remark the difference between the present and past participles in this respect.
The intransitive "to sleep" (no transitive usage) gives us the common adjective, "the sleeping princess," but "the sleeped princess," and "She is sleeped " are not used.
(In the sentence "She is sleeping," I don't think "sleeping" is an adjective, but rather a present participle as a component of the present continuous tense:
She sleeps; She is sleeping; She does sleep.
I think "to be plus adjective" would be a bit of a stretch here.)