I was recently watching a TV sitcom where a character had been deeply offended by her friend. After a full day of nursing her resentment, the character realized the rude event never happened—she had only dreamed that it had. Like the flip of a switch, her misery vanished.
It reminds me of the parable of the man walking outside during twilight. He shrieks at the sight of a coiled snake and runs, tripping on a stone and breaking his leg. A neighbor overhears his cries and comes out with a lantern. Holding the light up, it reveals not a serpent, but a pile of coiled rope.