I think the point I was making is different. It was that perception and experiences are real, just not necessarily reflective of a shared reality. The state of consciousness is much more than just the processing of external signals.
> if you have a solid source or line of thought that manages to explain one's sense of reality being more than «it's how I feel it for me, so that must be true of others, otherwise it's quite scary», I'm really (really) interested.
The best example I can think of is a dream. Dreams are real experiences despite not being shared with any other human. It would be absurd to say that you can't have dreams because they aren't perceived by or true for other people. The same holds true for thoughts and feelings.
People don't get sent into an existential crisis because they feel happy while someone somewhere is unhappy. Having a feeling is a real experience, despite being personal and subjective.