Plot hole
First of all, I don't start a thread about a plot hole with impunity but this is pretty glaring.
There is no way that he traveled down the river the way he did, going through rapids (indicating a significant decline in elevation) and then to a slower moving section with slow background music (indicating in movie speak a significant amount of time and travel) and then unknowingly crawl back to where the car was.
I suppose it is not completely impossible but he would have had to crawl for days in an upward direction to get back to where the car was. Why would he reverse his direction after he has been crawling downward to the river and then swept down the river to a significantly lower elevation?
It made no sense either that he crawled downhill from the car when the quickest way out would be to crawl upward to find a road. Cars don't end up crashed on the side of a mountain because they were driven up from below. Even in his deranged state he would have been able to figure that out.