Any good reading material on shared hallucinations? Some examples include similar dream archetypes (falling, being chased), sleep paralysis hallucinations like the old hag and abductions, and people claiming to see machine elves on certain types of hallucinogenics. I'm not looking for schizo-tier "ooh we're communicating with higher beings" bullshit, but rather books or studies that examine these shared hallucinations across cultures and time.