I 'spose you can guess that I'd suggest that what you 'know' is your subjective experience, rather than the source of it or that it represents 'fact'.....

THere are many, many things that can only be known through subjective experience. I suppose it could be argued that nothing can be known except through subjective experience. That's what you get for being a human being.

Consciousness is still very much a mystery -- an area science (ie neurobiologists) is only just beginning to investigate. And with great difficulty; as you say, as the subjective experience of consciousness is, by it's very nature, quite outside the realm of scientific empirical peer-approvable 'fact'.

But as to 'knowing' the 'source'??   HA!!! I highly, HIGHLY doubt we'd be having this conversation if I 'knew' that particular 'source'!