Continuity mistake: When the psychic collapses, sun is streaming through the window, indicating early afternoon. When we see the ambulance driving away a few scenes later, it's dark outside. It's highly unlikely it took a medic team several hours to get there and stabilise her.
Factual error: Scully reads to Mulder from a book all about flukes (Trematodes). However, the information she is quoting is wrong. She states that flukes or flatworms have a "scolex" with hooks and suckers. These are actually the distinguishing characteristic of cestodes (tapeworms). Trematodes have no scolex and definitely no hooks.