One of my first DXM trips was together with some DPH because it was usually recommended to take some against the nausea (which I shouldn't get but I didn't know that back then), I think it were just 50 or 100mg's of DPH. I was listening to psytrance music and heard a deep voice telling me not to be afraid and to let myself go - thought it to be lyrics but when I listened again to that disc there were no lyrics. After that voice I got surges of euphoria and a long lasted anxiolytic effect after the trip. But some time later I took DPH alone, 500mg, and it was just a weird, gummi-like body high and sedation. Thankfully no spiders. DPH is certainly a weird substance. Never took it again because it didn't help me to induce sleep like doxylamine or hydroxyzine do.
But you might be into something about euphoric DPH experiences, I think even scopolamine has been studied as a rapid acting antidepressant (in animals, of course). But I think it might just be the memory inhibition which lets one forget a bit similar to how people forget on alcohol, and not an actual antidepressant effect. In the end they use relatively simple animal models like the forced swim test to determine antidepressant effects and I'd imagine that a guinea pig or a rat would continue to try to escape an inescapable situation for longer when memory formation and recall are inhibited.
Also are anticholinergics even in occasional use linked to dementia.
