Excerpted from "The Bliss of Inner Fire: Heart Practice of the Six Yogas of Naropa" by Lama Zopa Rinpoche, Wisdom Publications. pp 148-9
Found this interesting:
"Because Kundalini is the main resource that we use in inner fire meditation, it is important for both males and females not to lose their sexual energy. Naturally, as beginners, we will find it difficult to control the energy when we experience it strongly; we have limited concentration and have not yet learned how to bring the airs into the central channel.
As Lama Tsongkhapa explains, it is not good to lose too much kundalini energy during meditation, but it is natural to lose a little occasionally. Don't panic and think, 'Oh, I have lost some kundalini energy. Now I have broken my vows.' When you are a beginnner, you sometimes lose kundalini drops. Don't worry about it. I lose it sometimes, and I don't worry about it.
Losing a small drop of liquid during your meditation causes no real damage or loss of strength. It does not make you unable to facilitate the kundalini. However, experiencingin orgasm through sexual contact or during sleep will cause loss of this facility and damage your strength. You can discover this through your own experience. When you lose kundalini energy strongly in meditation, the significant point is not that your are breaking your vow but that you are losing the strength of your kundalini. The physical exercises and concentraion will help you to develop control.
Control of kundalini energy is important even in ordinary orgasm. You cannot have a perfect orgasm if you cannot control your energy. It is the same in tantra. You cannot experience perfect bliss if you cannot control your energy. The fact is that if we lose our energy, we have no energy to utilize. In order to use energy, we need energy. If we don't have it, we cannot use it. This is logical, and you can see it clearly from your own experience. When you concentrate well and control your energy, you can experience more bliss, which you then unify with the wisdom of nonduality.
If kundalini starts to flow uncontrollably during your meditation and you begin to experience orgasm, try as much as possible to hold it and have it expand inside the secret chakra. Try to hold the energy there as long as possible. The longer you can hold it, the more pleasure you will experience and the more possibility you will have of utilizing that pleasure by unifying it with the universal reality of nonduality. In this way, you learn to control your body as well as your mind.
By the way, the semen that comes from the male sex organ during ordinary orgasm does not come from the central channel. For both males and females, the energy and bliss of ordinary sexual experience does not come from the central channel. you should be clear about this. The bliss of ordinary orgasm is produced by the kundalini touching the outside of the central channel.
In the logic of tantra, if the kundalini energy generates such bliss when it touches the outside of the central channel, there is no question that it will generate incredible bliss when it flows inside the central channel. Bringing all the winds into the ventral channel gives rise to an experience of incomparable super-bliss.
Drawing the airs into the central channel and activating this bliss is mainly accomplished through the power of concentration. Therefore, someone who loses kundalini energy because thery are living the normal life of a layperson can still be successful in the practice of inner heat yoga as long as they can maintain strong concentration during inner fire meditation. This is logical. Naturally, those who have weak concentration and also lose physical energy in this way will find it difficult to generate strong blissful energy. "