Consciousness is definitely not an all-or-nothing thing, though I suspect we only typically have access to very narrow band of potential levels of awareness (and can't control it "at will" anyway). But obviously there are some thresholds over which memories are simply not preserved in a sufficiently cohesive form for us to have any sense of maintaining consciousness, and in fact the point at which our brain stops being able to store recallable memories is surely the point at which our consciousness "stops". Having said that, clearly even in a dream state our brains have some ability to store memories, it's just that they're not memories guided by our normal capacity to process external stimuli, as are waking memories.

I'm not actually sure I would agree on not being able to store recallable memories being end of consciousness. Alzheimer and other medical conditions might very well result being unable to make new memories, but processing and reacting to stimuli based on old memories is still possible.

Reasonably I think stop of consciousness is both not storing and not reacting to.

I'd say Alzheimer's is essentially the inability to lay down memories that can be recalled beyond a very short period of time (in extreme cases, seconds). But once your brain can no longer store ANY recallable memories, you're unconscious.

Can you react to stimuli without being able to store any recallable memories? At least somewhat more complex stimuli than pain or bright light.

Sure, I would say it happens quite a lot (certainly while we're infants).

My only point is that to be conscious is tautologically to know that one is conscious. And knowledge is dependent on having (= being able to recall) a memory of something. Yes, colloquially there are instinctual forms of 'knowledge' where you get some vague sense something must be true (despite having no information to determine one way or another), but I'd suggest that's probably a misuse of the term.

I was a first responder for a while and we would record a metric called "Level of consciousness" often abbreviated as LOC - it was rated "times 0" to "times 4" based on how aware of your environment and able to respond to stimulus that you are

https://en.wikipedia.org/wiki/Altered_level_of_consciousness Here's a better source with more levels

The word 'stuporous' is definitely ripe for going viral.