Ok, you got me thinking, and now I gotta post.
If I were to guess, I'd say the effect is probably physiological instinct taking over, as it were. This would wax and wane with time and *cough* activity, and would be contrasted with and replaced by the cool logic that uses reason rather than impulse.
As a Christian, I'd think this is what Paul was referring to when he spoke of our dual natures being "at war" with each other. Logic and impulse are obviously incompatible modes of thinking. "Flesh" and "spirit" are disharmonious, mutually exclusive, and helplessly stuck together.
“But I say, walk by the Spirit, and you won't fulfill the lust of the flesh. For the flesh lusts against the Spirit, and the Spirit against the flesh; and these are contrary to one another, that you may not do the things that you desire. But if you are led by the Spirit, you are not under the law. Now the works of the flesh are obvious, which are: adultery, sexual immorality, uncleanness, lustfulness, idolatry, sorcery, hatred, strife, jealousies, outbursts of anger, rivalries, divisions, heresies, envyings, murders, drunkenness, orgies, and things like these; of which I forewarn you, even as I also forewarned you, that those who practice such things will not inherit the Kingdom of God.
But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faith, gentleness, and self-control. Against such things there is no law.” — Galatians 5:16-23
Not trying to say sex is bad, or anything. Just trying to draw contrast between naturalistic impulse which governs the animal kingdom and our priceless gift of logic and reason. It's what this thread reminds me of anyway when speaking of human duality. It also ties into morality in that self-control is born from reason not impulse, and is therefore forced to compete directly with our physiological instincts.
