Dana writes at The Edge of the American West:
On this night in 1619, after a night in which he swears he was not carousing, René Descartes went to bed in an overheated, stuffy room in Ulm, and had three vivid dreams to which he later attributed the eventual course of his life.
In the first dream, a strong wind battered Descartes, and he sought shelter in the church of a college, only to be pushed back by the winds. After the winds abated he found himself surrounded by upright people, while he himself tottered along, leaning to the left. In the second dream, he perceived a loud thunderclap and saw the room filled with sparks of light. This apparently was a recurring dream for Descartes, so he meditated on logic until he fell asleep. (It’s like counting sheep, but for intellectuals.)
In the third dream, Descartes felt no terror, but instead came upon a book of verse, the first line of which read “Quod vitae sectabor iter?” and another poem, presented to him by an unknown man, with the first line “Est et non.” Which way of life shall I choose? It is and it is not.It’s no tolle lege, but it’s surely proof that the universe has a sense of humor, having man who would be identified with rationalism and whose books and teachings would be periodically banned, get his inspiration from a dream about a church...
One can read Descartes' Meditations in the original Latin here (You can also read it in English, if you must).