Explanation of the Movie - SPOILER

Rather than explain various plot points in different threads, I thought I'd offer an overall explanation of the film here. Since THIS IS A SPOILER, I will mark it as such. Hover your cursor over the blacked-out area to reveal the text.
Once it is revealed at the end that Sam and Lila are trying to save Henry, the viewer learns that the entire film up to that point has been all from Henry's perspective and in his mind. The reality is, Henry was driving, and he had plans to propose to his girlfriend who was in the front seat with him. In the back were his parents. He realizes he has been in an accident, and believes he caused it. He also recalls his girlfriend going through the windshield and that his parents are dead. Coupled with those facts, are two strangers on the scene - Lila, who is really a nurse; and Sam, who is a doctor. Onlookers are gathering around, including the one kid who asks his mom, "Is that man going to die?"
Anyone who has ever left the television on while very sick, knows how subconscious and reality merge, creating some really funky dreams. That is what happens to Henry. Everything around him, his reality, is merging with his memories and his subconscious. He puts Sam and Lila together as a couple, when in reality they've never met. Sam is trying to save him, yet Henry is looking for answers. Thus his subconscious puts Sam as a psychiatrist. Henry is an art student, and as he dies, he wonders if he'd ever have been successful. He bounces in his dream state between being himself and being Henry - when he is Henry, he is asking all the questions he'd have regarding his own self-doubt. He feels he has killed everyone and now himself (thus suicide in his dream state.) It is his 21st birthday, he planned on proposing to his girlfriend, and it is almost midnight. In his dream, he has decided he will die at midnight on his 21st birthday. His dream/drifting consciousness takes place in the few minutes immediately following the accident, and just like any dream, the time feels like hours or days. Once Henry is told that the accident is not his fault, but rather due to a tire blow out, he dies in peace.