Meditation 1
...I will suppose that some malignant demon, who is at the same time exceedingly potent and deceitful, has employed all his powers to deceive me; I will suppose that the sky, the air, the earth, colors, figures, sounds, and all external things, are no more than the illusions of dreams, which this being has used to set traps for my credulity; I will consider myself as without hands, eyes, flesh, blood, or any of the senses, and that to believe I have these is false...
...But this is a hard undertaking, and a certain indolence leads me back, without knowing it, to my ordinary course of life; just as the prisoner, who, perhaps, was enjoying in his dreams an imaginary liberty, when he begins to suspect that it is just a vision, dreads awakening.
Meditation 2
The Meditation of yesterday has filled my mind with so many doubts, that it is no longer in my power to forget them. Nor do I see, meanwhile, any way in which they can be resolved; and, just as if I had fallen all of a sudden into very deep water, I am so shocked that I cannot either plant my feet firmly on the bottom or sustain myself by swimming on the surface.
René Descartes, Meditations on First Philosophy 1, 2