At the end of Supernatural season 3, Dean Winchster was sent down to Hell, and after his return, revealed how time works there when compared to Earth. From the beginning of Supernatural, the Winchester brothers were encountering - and taking out - demons. This established right away that there must be a Hell in their universe, as the demons had to come from somewhere. As the seasons drew on, Sam and Dean actually ended up getting pretty used to visiting Hell, sometimes even under friendly circumstances.
It wasn't until Supernatural's season 3 finale, "No Rest for the Wicked," that either of the Winchesters went to Hell in person for the first time, and it was under particularly bad circumstances. Sam had been killed, and Dean had made a deal with a crossroads demon to resurrect his brother, in exchange for his own soul. The pair spends most of season 3 trying to find a way to break this deal, but in the end, Dean is killed by Hellhounds and is sent to Hell, presumably for eternity.
While Dean is rescued from Hell by the angel Castiel - in an arc that would introduce one of Supernatural's most popular characters - his time there still took its toll, both physically and mentally. That's especially true thanks to the strange way time works in Hell.
Supernatural: How Time Works In Hell (Based On Dean's Trip There)
After Dean is rescued from Hell by Castiel in season 4, for the longest time he understandably doesn't want to discuss his literally torturous time there, even with Sam. When he finally opens up to his brother, Dean explains that while to Sam only four months had passed between Dean's death and resurrection, to him it felt closer to 40 years. He spent 30 of those years being horrifically torn to pieces and rebuilt, before finally succumbing and becoming a torturer himself, to his great shame. That means every single day on Earth felt like four months of torture to Dean. No wonder he's so messed up about it, although he did seem to recover rather quickly once that plot ran its course.
Not that it's a competition anyone wants to win, but Sam actually got it even worse. While Sam never applied an exact figure to how long he had been locked in Lucifer's Cage between the end of season 5 and his soul being recovered from Hell, and Hell doesn't necessarily have any laws of space and time, we can extrapolate a time frame based on Dean's experiences. It's unclear exactly how quickly Sam's soulless body was raised from Hell, but it's known that he waited about a year to contact Dean afterward, and even more months passed before he got his soul restored.
For simplicity's sake, it can be estimated that Sam spent between one and two Earth years in Hell. That means he was stuck in a cage with an angry and vengeful Lucifer and Michael for what must've felt like between 120 and 240 years. Considering that, it's a wonder he ever recovered mentally at all. Thankfully, both brothers did eventually make it to Heaven in Supernatural's series finale.