I know you’re kidding, but please nobody do this. Taking that much diphenhydramine is going to give you terrible nightmares. It will also leave you feeling remarkably hungover - to a greater extent than alcohol. You’re also getting dangerously close to the territory of inducing a hallucinogenic trip at that point. I’m not exaggerating.
Diphenhydramine, much like “DXM” (the main ingredient in cough syrup) is a powerful hallucinogen when taken in the right dose. Except it has no recreational value whatsoever. It’s basically just a prolonged psychotic experience. It isn’t pleasurable at all the way something like LSD or magic mushrooms are.