A rare illness caused by a breakdown of neurochemical molecules during transport, producing delusions and physical decline, largely eliminated by improved pattern buffers in the early 24th century.
Transporter psychosis is discussed in the Next Generation episode Realm of Fear. Reginald Barclay, who has always dreaded the transporter, sees worm-like shapes in the matter stream and looks up the condition in the ship's computer.
The entry says it was first diagnosed in 2209 by researchers on Delinia II. Victims suffered paranoid delusions, hallucinations, hysteria, sleeplessness and dehydration, and no case had been recorded for more than fifty years, since the multiplex pattern buffer was perfected.
Barclay convinces himself he has it and reports to sickbay. In fact his symptoms come from quasi-energy microbes, and the shapes he saw were the crew of the USS Yosemite trapped in the beam.