Mystique in the mirror

At first, Alan was just an ordinary young man with memory problems.

But then Alan's life changed after he saw the ghost of a strange old man every time he looked in the mirror.

Because his father thought Alan was hallucinating, Alan entered treatment at a psychiatric hospital, hoping to recover and return to his father.

But there, Alan found a skeptical document stating that his father had long been dead (?)

Alan thought he was hallucinating.
Alan thought he was just sick.
Alan thought that once he recovered, he would go home.
But in reality, he was wrong about everything.