- Omphalos hypothesis
Descartes' "evil demon"
"Brain in a vat" hypothesis
The problem with them isn't so much that they are false/unlikely, but rather the combination of their being unfalsifiable and (if true) causing all other knowledge to be valueless.
Or rather, that in the end they don't much matter. If it's true that we're in a simulation, for example, then statements about the nature of reality don't become meaningless, they just become statements about the nature of our simulated reality. If we're in a dream, then statements about reality become true statements about our dream world. And so on. And any statement about the nature of the unsimulated reality beyond us has no hope of being anything other than speculation.
These are my own personal musings, but I would imagine that they're pretty standard and also that I absorbed them from somewhere. So I'm wondering if a) there is a standard philosophical treatment of these ideas, and b) if there are holes in what I've presented here.