Field Trip

Looks like someone spilled tons of mustard in the fake shower. ^Wait...

Written by Frank Spotnitz (Story), John Shiban (Teleplay), & Vince Gilligan (Teleplay)
Directed by Kim Manners

"They're affecting your head... maybe mine, too. What if I can't even tell what's real?"

— Wallace Schiff

Mulder and Scully investigate the mysterious death of a couple whose skeletons were found in the forest.

Tropes:

A Glitch in the Matrix: Both Mulder and Scully realize at various points that things are not what they seem and that they are in a hallucination.
Double-Meaning Title: "Trip" as in "expedition" and as in "hallucinatory experience".
Dream Within a Dream: Mulder and Scully realize the mushroom is causing them to hallucinate and snap out of it... except, not really.
Fungus Humongous: The episode features a giant underground fungal complex; the non-sentient growth sucks down its human victims and doses them with powerful hallucinogens to keep them docile while it slowly digests them.
Mind Screw: Bizarre things happen inside Mulder's and Scully's hallucinations, such as the Lone Gunmen believing Scully's case report, as well as Mulder retrieving an alien from the cave.
Monster of the Week: A very dangerous fungal complex.
Mushroom Samba: The spores Mulder and Scully are exposed to for most of the episode are said to have similar effects to LSD.
Schrödinger's Butterfly: There's no way to be sure that the final scene in which they were rescued is real. It's possible that it wasn't, but they were still ultimately rescued, as people knew where they were going, and their vehicles were parked in the open not far away. It's also possible that they were never rescued and the entire rest of the series is their extended hallucination as they lie dying underground.
Together in Death: In the teaser, a couple is shown cuddling and lying together in bed facing each other. The final shot of the teaser reveals they are already skeletons.

Once you leave this webpage, reality awaits! But before you press that button, we would like to leave you with one important message: TV Tropes will always change your life for the better!

Wait a second... WHAT WOULD POSSESS US TO EVEN SAY SOMETHING LIKE THIS?! TV TROPES WILL CONTINUE EATING AWAY AT OUR LIVES FOREVER! ...Come to think of it, is something else eating away at us now?!

^{And the headache comes again...}