Gen, Sam and Dean trapped in a cave
As time goes by and infection sets in/dehydration takes its toll, Sam (mistakenly) begins to assume that he will die and it is what Dean would want, because of John's prediction that Dean will have to kill Sam.
Eventually they do get rescued, and Dean needs minimal treatment, but Sam is near death and is hospitalized. Dean is furious in a protective/worried way, because they was still plenty of water to spare that Sam could have consumed or used to clean his leg.
Sorry, I know this is very specific but no matter how much I search, I can't find it.