Delirium

That's exactly where our main character (Topher Grace) is. He returns from a mental institution to the family mansion he inherited from his parents. But because his release from the institution is only conditional, he must report regularly to his probation officer and not leave the house for thirty days. Otherwise, he faces further internment in a psychiatric ward. And he definitely doesn't want to go back there. His psychiatrist gave him medication to take regularly and a piece of advice: "Trust your mind, not your eyes." But in an abandoned house filled with memories, he finds unexpected surprises. Subtle at first, yet quite explainable by common sense. But as memories begin to materialize and other paranormal phenomena unfold, he begins to question his sanity. Is he really alone in the house? And if he's not, are there real people hiding in there, or are they some scary phantoms he's conjured up in his head? What of all this is actually real?