I've recently tried to stop using the term "sentient being", and instead prefer the term "sentient perspective". This reminds me of that.

If you think of a river's current as representing a more universal sentient perspective, then you can see how an eddy in the river could represent a different sentient perspective, from which you could not actually tell the direction that the rest of the current is going - similar to the "event horizon" you mention further down.

So perhaps the questions we ought to ask about sentience aren't how it is "generated", but rather, what type of constraints on the universal sentient stream lead to different "types" of perceptions (i.e. "qualia") for the smaller, "subjective" eddies.