In The Machinist, we see Trevor Reznik go to the amusement park with Maria (the waitress) and Nicholas (her son). Trevor and Nicholas go on the Route 666 ride, and Nicholas has an epileptic fit.
Later, we find out that
Nicholas was the young boy that Trevor knocked down and killed, and that Maria was never his waitress at the airport - he hallucinated both in his guilt. However, this scene sets up Trevor to remember more "ghostly" memories, and triggers his deteriorating relationship with both Maria and his other love interest, so it's clearly pivotal in his reconciliation.
So, this begs the question: did Trevor really go to the amusement park? If he did, who did he go with, if anyone? Did he go on the ride, or was it a figment of his imagination?