Xanax doesn't have any anti-cholerigenic properties so you wouldn't see any Benedryl spiders. That much xanax would be more comparable to the weird visual effects liquor where it can definitely make you see some weird shit, but it would be more like a false sleepwalk than an anti-histamine trip.
The ACTUAL way to speedrun the spiders is Ambien and Doxylamine.
I mean Xanax is an interesting one to make this joke about because if you don't mix it with anything, you can't take enough Xanax to kill you. People that take that much wake up in jail or a mental institution from the ensuing psychosis, but not dead. And you don't really see the hatman or any of the "fun" psychosis hallmarks, it's more like it hits and you're just vibin on the Skyrim load screen until you wake up and hear "You're finally awake".
Yeah main innovation that benzos introduced were how not deadly they are on their own. Imagine the amount your breathing slows down on downers as a number starting at zero when you're not on anything. A standard downer is gonna add to that number, like a beer would add 5 or an Oxy would add 30. This is not how benzos do respiratory depression though. They multiply that counter. At 0? Okay cool, 0x100mg of Xanax is still zero, you'll be fine. Wake up in jail or a mental ward, but physically fine. This is all to say do not mix benzos with other downers because that's the difference between dying and just doing something stupid.