I feel like a man who has fucked too much (forgive me for the expression) - a kind of rapturous lassitude.

From a letter Flaubert wrote to the poet and novelist Louise Colet, his sometime-lover, on December 23, 1853, at 2 AM:

I must write to you tonight, for I am exhausted. My head feels as though it were being squeezed in an iron vise. Since two o’-clock yesterday afternoon (except for about twenty-five minutes for dinner), I have been writing Bovary. I am in the midst of lovemaking: I am sweating and my throat is tight. This has been one of the rare days of my life passed completely in illusion from beginning to end. At six o’-clock this evening, as I was writing the word “hysterics,” I was so swept away, was bellowing so loudly and feeling so deeply what my little Bovary was going through, that I was afraid of having hysterics myself. I got up from my table and opened the window to calm myself. My head was spinning. Now I have great pains in my knees, in my back, and in my head. I feel like a man who has fucked too much (forgive me for the expression) - a kind of rapturous lassitude. And since I am in the midst of love it is only proper that I should not fall asleep before sending you a caress, a kiss, and whatever thoughts are left in me. …

Source: Madame Bovary: A Norton Critical Edition (second edition), edited by Margaret Cohen, p 307. Letter translated from the French by Francis Steegmuller.