City on the Edge of Forever (South Park)
The bus falls off the cliff into a tub of ice cream, and Cartman wakes up in bed.  He realize he was dreaming the whole time.  Then Stan wakes up in bed, and he realizes he was dreaming about Cartman having a dream. The last scene shows Ms. Crabtree and Marcus.  Ms. Crabtree knows it is all a child's dream but wants to enjoy it while she can.