Here's a story courtesy of Japan's master of horror Junji Ito. Remember to read from right to left. Also, this is 1/3 of a 34 page story.
It turns out the patient that was walking through the halls is Tetsuro Mukodo, who's been suffering from "long dreams".
He goes on to say that the dreams have increased in length, now lasting years at a time. The doctor thinks he's lying or is suffering from a mental disorder that makes him believe the lie. He decides to observe the man's sleeping patterns.
The man's dreams grow increasingly longer--now he's dreaming for ten years at a time. One dream is him spending years studying for an exam, the other is ten years in the jungle fighting a war.
Soon his body begins to physically change as if he is evolving over an extended period of time:
He believes that he's been married to Mami (the girl from the opening scene) for thousands of years. When she sees him, she screams, thinking that it's death come back to claim her.
Soon his body begins to crystallize and break down.
From the crumbled remains of his brain, they discover small crystals of unknown properties. They attempt to analyze them to discover the link between the long dreams but to no avail.
Soon the girl, Mami, tells the doctors that she is experiencing long dreams of her own--dreams that last months at a time.