A similar claim was made by Norman Malcolm quite some time before Dennett, as he is aware, and this claim was based on Wittgenstein's logically positivistic verificationist approach, which involved the concept that the meaning of a statement is determined by its use, and that if a claim is not verifiable or falsifiable it's meaningless. Malcolm claims that because one cannot assert that one is asleep while asleep, dreams are not experiences. This is of course problematic given that there are lucid dreams. However, it certainly seems problematic to assert that an unrecalled dream is an experience as there would seem to be no way of checking this. A sleep researcher might detect REM or an EEG trace characteristic of sleep, but that's not the same as an experience.
My own view on this is that it connects to the relationship between states of consciousness and reality. Wakefulness is one kind of relationship with reality, which for instance involves linear time and a close temporal connection between events and their experience and the will. Dreaming sleep involves a different relationship - there's a connection between the events perceived as linear by wakefulness and the mind, but of a different kind. I don't consider any states of consciousness as having priority over each other, i think. Hence research done while awake on a dreamer is merely research done wakefully rather than a clinchingly accurate judgement, as it cannot compete meaningfully with dreaming. The same applies to research on one's own dreams while awake. What would research on wakefullness while asleep look like?
I see there as being around five or six states of consciousness, none of which have priority. In them, one has different relationships with phenomena. Psychotic experience seems to mix them.
This was rather waylaid by not having finished Dennett's essay before i made the video. I had further thoughts on the relationship between states of consciousness and time after i finished it. So far, it has two views. Two! I can allow myself a factorial there since 2x1=2. Maybe it's because i misspelt "wakefulness". It might pick up i suppose.
I think i need to go through the analytics and find out what's likely to be popular. It generally seems to be gender-related stuff. For some reason, the silicon-based life form video is a lot more popular than the other aliens vids though, so there's a different problem there, possibly to do with sharing or getting picked up by, what are they called, link aggregators?