The Tilonus Institute for Mental Disorders is a hospital on Tilonus IV, for psychiatric patients.
In 2369 Commander Riker was kidnapped and made to believe he was a patient in ward 47 at the Institute.
Doctor Suna, a psychiatrist there, tried to convince Riker that his being a Starfleet officer was a delusion, just a series of hallucinations that started after he stabbed a man in cold blood.
While there, he also met a woman named Jaya who also claimed to be a kidnapped Starfleet officer, "Commander Bloom of the starship Yorktown". He soon realized that she really was a psychiatric patient however, when she tried to use a spoon as a communicator. (TNG: "Frame of Mind")