I searched the Corpus of Contemporary American English ( https://www.english-corpora.org/coca/ ) for 'conscious_n', which means the token "conscious" with a 'noun' part-of-speech tag.

There are five results. All five of them are tagging errors:

If we scan to get enough info, then model the cells well enough, and have enough computers to run the simulation of the models, then the input-output of the emulation of the brain will be the same as the input-output of the original brain. It will act like it is conscious. [adjective, modifying it]

Well, first we work on working the body together, so that we can go places with both of us conscious. [adjective, modifying both of us]

Lady Bertram looks barely conscious. [adjective, modifying Lady Bertram]

In a few years, he believed, this institution would be needed in Ukraine, as new conscripts became more religiously conscious. [adjective, modifying new conscripts]

It is in this sense that Rahner means that grace is conscious. [adjective, modifying grace]

Examples 3 and 4 are so far from being nouns that they're being modified by adverbs.

It seems safe to conclude that in fact there is no nounal use of the word "conscious".

> Adjectives sometimes become nouns this way, like "the poor"

That isn't actually what's happening in "the poor". The position occupied by the token poor in that phrase can be filled by all kinds of things:

God loves everyone equally. The rich and the poor, the just and the unjust, the sane and the schizophrenic, the possessed-of-billions-of-dollars and the penniless...

Do you want to argue that "possessed of billions of dollars" is a noun?

We can apply our in-passing observation from earlier and contrast the fully-awake with the barely-conscious. Here, as above, it's impossible for conscious to be a noun, because it is being modified by an adverb. And it's... dubious... for barely conscious to be a noun phrase, because it is headed by conscious, which we know isn't a noun.