Pain is life's reminder that we exist.
Painless expanses of time melt together into a non-descript state of reverie, supreme happiness a drug that dulls the senses, never restoring them until the happiness be smitten. The sensation of happiness is not unlike the feeling of dreaming a sweet dream, the covers separating one's body from the cold, harsh elements that lurk; but wherever they lurk it's far from here, we don't know them and we couldn't name them. Because they don't concern us.
What is commonly believed to be the test of whether a person is dreaming? Pain. The pinch that brings the subject back to reality, back in touch with the things they had forgotten about, the things they neglected in their intoxicating bliss. We are weak, vincible, mortal. We are bound to a frail system of tissue and fluids. We are subject to involuntary states of consciousness that we call feelings, at times unconquerable by the strongest will.
Yes, we definitely do exist, of this much I can be sure...