Is it normal to overthink when you're high?

I would have to agree with you for most of your reasons, but cannabis isn't just a stimulant. It's overall a psychoactive drug, but has effects pertaining to either stimulant, psychedelic or depressant so it couldbe hard to really pinpoint the exact cause of it just because of the type of drug, but ive had the same experience as the question-asker in this case. I learned to just hang out and toke with people who i know aren't fake and who i can trust.