Jerry fights his own foot
I wonder if he actually DID stumble into the entrance of Glastonbury Grove? Check out the long shot at 33:37. It looks like he's in a clearing surrounded by trees. He also appears to have stepped into a shady or "oily" patch?
All this, and he's probably high? Now that's a double dose of dark comedy!
How long has Jerry been lost in the woods!?
Hey, there may be something there! It really does look like he's in the same high as when he called Ben. At least one day has to have passed for Ben, but did it pass for Jerry too? Considering Buckhorn/Gordon team seem to be August 20th and Hawl team August 29th, as of Part 9, maybe Jerry is in a different time frame too.
Someone in the "Bang Bang Bar Chicks" thread proposed the idea that Zebra, which the two girls in the roadhouse at the end of the episode mentioned was back on the streets or something, is a designer drug (wasn't something about Chinese designer drugs infiltrating Twin Peaks mentioned earlier in the series?) that somehow gives you a kind of access to the Red Room (black and white chevron floors...Zebra...)...
Maybe Jerry, clearly being a man chasing altered states, got ahold of this drug and, as he said over the phone to Ben, "I think I'm high!" He feels high because he's suddenly in a very psychedelic and bizarre state... Maybe this drug dissolves the boundary between dimensions, between Twin Peaks and the Red Room, for instance...
Also reminds of the many references (e.g. Leary in The Psychedelic Experience, Sam Harris in Waking Up, Grof & Halifax in The Human Encounter With Death) to psychedelics opening the gates to heaven and hell, and recent research by Roland Griffiths and Robin Carhart Harris into the link between psilocybin and mystical experiences.
On a re-listen it sounds like Jerry's own voice distorted. Not exactly like the evolved tree (voice apparently uncredited). Agreed? Another? Impossible to tell?
If his own, I take it as cuing drug-induced hallucinations rather than contact with beings from alternate realities, though I guess these aren't necessarily mutually exclusive.