Most people do have a memory of what it was like to be dreaming, at least some of the time. And some people have vivid, detailed recall of dream narratives -- I dated one for four years. Even in her summarizing mode she could go on for ten minutes about one dream.
Going back to your main theme -- there are people who know they experience pain, and will grant that other humans experience pain. But because fish are so different from humans, their aversive behaviors when snagged on a hook, or gasping as they suffocate out of the water are attributed to reflexive action and is absent pain. Sure, I can't know what their experience is like, but if it looks like a duck and quacks like a duck, etc, it is likely a duck. The same applies to consciousness of advanced artificial neural networks.
They were talking about anesthesia, its a different state to a dream state. When you fall under anesthesia you just shut down - no experiences of any kind - and next thing you experience is waking up.
> Because we don't don't have any memory of what it was like to be in these states.
I want to add an anecdote from about 5 years ago when I fainted: there is a tiny moment as I was regaining consciousness that I had an experience that is unlike anything I’d ever experienced before (and words really fail to describe it) there was no sense of time, or even presence- it was like pure observation. It wasn’t the blackness nothingness that I think is associated with being unconscious, instead it was the opposite- it felt like hundreds of images, sounds and thoughts all layered on top of each other- it was very ‘noisy’. That might sound stressful, but I don’t remember feeling anything at all.
It was only when some of that noise faded away that I experienced a sense of ‘self’ again and a moment later I formed the idea where am I? And then I opened my eyes and everything was back to typical conscious experience (although feeling a little disoriented).
I'm in the camp that says this question is unanswerable. We know we individually are conscious because we experience it. We accept that other people are conscious because they are so similar to us and they say they are, so by Occam's Razor they aren't zombies and they aren't lying. We haven't proven they are conscious, but we accept it. It seems reasonable. But if our test is just that it seems reasonable, there will be no convincing someone that a very dissimilar thing isn't just lying or faking it.
We say some things are not conscious not because we have evidence of this, but because the test is whether we ourselves say "Yes, this is conscious."
Furthermore, we hold onto this distinction as important because it has ethical consequence. We can do what we want to things that aren't conscious, so it's important that as many things as possible not be conscious. Is that thing conscious? It depends. Does it taste good?
One more thing: we say we are unconscious under anesthesia or when we are asleep. Why? Because we don't don't have any memory of what it was like to be in these states. But this is a test of memory, not consciousness. I don't have memories from when I was one year old, but I'm fairly certain I was conscious then.