In Slaughterhouse Five, the protagonist, Billy Pilgrim, suffers from PTSD caused by the mental trauma of having been in the war. He deals with this by imagining that he has come unstuck in time and can relive various moments of his life in whatever order he pleases. In the novel, because of this ability, Billy knows the exact manner and time of his death.
...Billy Pilgrim says now that this really is the way he is going to die, too. As a time- traveler, he has seen his own death many times, has described it to a tape recorder. The tape is locked up with his will and some other valuables in his safe-deposit box at the Ilium Merchants National Bank and Trust, he says...
And just before his assassination,
'No, no,' says Billy serenely. 'It is time for you to go home to your wives and children, and it is time for me to be dead for a little while-and then live again.' At that moment, Billy's high forehead is in the cross hairs of a high-powered laser gun. It is aimed at him from the darkened press box. In the next moment, Billy Pilgrim is dead. So it goes. So Billy experiences death for a while.
How is this possible if Billy's time-traveling abilities were just hallucinations caused by PTSD?