If you are alert, sex will be impossible.
If a man is alert while making love, the more he is alert, the more it will be difficult.
He will not be able to get an erection.
It cannot be willed, and if you will it you will lose it.
The same method, the same technique, can be used in sex.
Just in the beginning, when you feel the sensation of an erection just coming to you but it has not yet come, you just feel the vibration, become alert.
The vibration will be lost, and the same energy will move into alertness.
Tantra has used this.
It has tried in many ways.
A beautiful naked woman will be there just as an object for meditation, and the seeker, the meditator, will sit before the nude woman meditating on her body, her form, her proportions, just waiting for the first sensation in his sex center.
The moment the sensation is there, he will close his eyes.
He will forget the woman.
He will close his eyes, and he will become alert of the sensation.
Then sex energy is being transformed into alertness.