Descartes' second dream:
"Having lain awake for awhile, Descartes fell asleep again and almost immediately had a second dream in which he heard a sharp explosive noise that sounded like thunder. This caused him to reawaken, and he saw sparks from the stove fire flying about the room. He remembered having had this experience before, while awake, and he was therefore able to make sense of it and to return calmly to sleep."
Desmond M. Clarke, Descartes: a biography