The conclusion to draw here is not that the world is unknowable.

I'm not say the world is unknowable. The world is knowable, but only through the senses, and mind.

The boiling point of water at sea-level is not something that exists in my head - it exists in the world.

The world (object) does not exist independently of the individual (subject). To know the boiling point (or the world at all) there must be a conscious subject. How the world exists beyond our senses is not known to us. There certainly is 'something' there underlying the mind, but is it identical to how our senses and mind interpret it? No, I do not believe so.

sorry, but that's just wrong.

It is my belief that facts are formulated and defined by the human mind, and that 'reality' is much different than what the mind perceives. You may think it's wrong, but it's a philosophically justifiable position. Again, your quip leaves me nothing to argue against.

I was making a point about any attempt to draw conclusions from such experiences, not refuting conclusions I thought you had drawn.

You seem to misunderstand what deep sleep is. Deep sleep is not an 'experience'. Experience implies the presence of the mind. Deep sleep is a state of consciousness without an object, yet we 'know' that state despite no object being present. You fail to see that deep sleep is an object of 'knowledge', without an object. It is a purely subjective state of consciousnesses. No proof for what deep sleep 'is like' is present in the world. You and other materialists try to argue that the qualitative aspects of experiences are reduced to material, however you cannot do that for the state of deep sleep, since there is no underlying object to derive the qualitative 'restful' properties which are intrinsic to the state. Thus, deep sleep is a purely 'subjective' state, which we know as being deeply restful without an underlying object. This gives important clues about the nature of consciousness.

That's precisely the "mystery" I see you asserting without grounds.

I'll repeat myself again. Sleep is not a 'mystery' at all. Just because something can't be described by objective means does not entail it's a mystery. There is no objective definition of what beauty is, but everyone knows what something beautiful looks like.

Even if true (and I don't accept that it's obviously true), the matter of interpretation, my original point, still stands. Any attempt to derive conclusions from this state inevitably goes through your mind and therefore through your conditioning.

Thank you! You seem to get what I am saying about epistemology here, but for some reason you think 'objective knowledge' is excluded from this conditioning... Yes, you are right the state is understood through the lens of the human mind, just like any other attempt to explain the world inevitably goes through your mind and therefore your conditioning. The state of a child, deep sleep, etc. are unconditioned because the mind is absent, however our attempt to describe and explain it is conditioned upon our return to waking consciousness.