Sam and Dean race to Bobby's side after he lapses into a coma and can't be awakened. While unconscious, Bobby battles his personal demons and the reason he became a hunter is revealed. Sam and Dean discover someone poisoned Bobby with a potion that will kill him if he doesn't wake soon. When the brothers decide to take the potion themselves to enter Bobby's dream in order to save him, they come face to face with their own personal nightmares. Source: The CW

Eric Kripe reveals: We actually spend a little more time with how Dean himself feels about going to Hell because right now he's accepting that he's going to Hell and he's unwilling to do anything to stop it. That changes 180 percent in Episode 10. Something big happens to him that makes him realize he desperately wants to live and he desperately doesn't want to go to Hell. Bella makes an appearance in a dream episode, where Sam and Dean take this medicine man drug where they go dream walking, which is going into other peoples' dreams. So we spend the majority inside Bobby's dreams, inside Dean's dreams. Source: TV Guide Online

Dean dresses in a suit and tie, pretending to be a detective, when he goes to interview students and faculty at a college. He asks one stoner student about the death of Dr. Gregg and the sleep study he was conducting, testing a treatment for a sleep disorder. The student has the inability to dream and says he quit after one session with Dr. Gregg because the stuff he gave him caused him to have a very weird, super intense dream, much like an acid trip. Bobby, Sam and Dean all get trapped in their dreams and figure out that the one causing it is Jeremy, the stoner student Dean questioned. Source: SpoilerFix.com

but heard that in ep11 dean got killed many times in many ways... and sam had to live that tuesday (i think it's tueday) over and over again at the same time watching dean got killed... poor dean...

Eric Kripe reveals: 'Mystery Spot' is a Groundhog's Day episode where Sam keeps reliving the same Tuesday over and over and over again, and at the end of every Tuesday Dean dies. And no matter what, it's actually a pretty funny episode. We killed Dean in every conceivable way. He gets electrocuted, he gets botulism, he's hit by a car, he's crushed by a desk, you know he's shot a couple of times, he's hit with an arrow. It's a totally fun episode. It's actually kind of meaningful, and we play - I think it hits what Supernatural does best, it's funny one moment and emotional the next. This obviously freaks the hell out of Sam, having to watch Dean die over and over again. Source: Kristin on E!Online

Sam and Dean investigate the disappearance of a man who went missing at a tourist location. While searching the site, Dean is shot and killed by the owner. Sam is devastated but stunned when he wakes up the next morning to find Dean alive and well. As the day unfolds, Sam realizes he is re-living the previous day and tries to prevent Dean's death, but to no avail. Dean dies again and Sam must learn to live life without his brother by his side. Source: The CW

Eric Kripe reveals: We also have a great Groundhog day episode coming up. Sam basically wakes up every day and it's the same day and Dean dies at the end of every single day. It's actually quite funny. Dean dies maybe 10 different ways on camera, and off camera, maybe he dies 200 different ways. Sam doesn't go through just three or four Tuesdays, he goes through something like 150 Tuesdays. Source: TV Guide Online