The Kechari Mudra

As distinct from the artificial application of the Kechari Mudra, what happens during its natural occurrence is not only that the tongue reaches behind the uvula and above the soft palate or roof of the mouth**, but that it can do so because the soft palate can retract on its own, thus enabling the tongue to naturally curl back upwards in order to reach up to the bottom of the base of the skull at the location of the sella turcica.

In the natural form of the Kechari Mudra the soft palate spontaneously 'pulls in' or retracts in a physical manner for a short period of time (from seconds to hours) thereby making the space (Sanskrit 'akasha') above the soft palate accessible to the tongue.
When that happens, the tongue then tends to want to touch, vibrate or lightly massage the bottom of the bony support of the brain. The resulting vibration, which also can be brought about (although more lightly) by snoring, humming, Tibetan chanting, singing, sounding the AUM mantra and sounds made during sexual intercourse can lead towards experience of:

Ecstasy,
Orgasmic feelings in the upper part of the body and head,
Exalted rapture,
Fully integrated physical, erotic, volitional, emotional, expressive, inspirational, conscious human/divine bliss,
Conscious participation in human-divine reality and human-divine activities,
Acute awareness of the immortality of one's being,
The experience of human-divine glory.

The application of Kechari Mudra as described in Hatha Yoga Pradipika (chapter III, sloka 32 - 53) is an artificial (but effective) way to bring this about by gently and over time severing some tissue underneath the tongue in order to enable the tongue to reach behind and above the soft palate and to bring about results that are nearly identical to the experience of amrita and rapture (the experience of immortality and highly ecstatic states) that come with the natural Kechari Mudra.
There are some challenges with the 'forced' Kechari Mudra: one can come close to suffocation, fall into a state of mortal fear and... there might be manipulative tendencies involved that can lead to 'self-absorption' and 'exclusivity at the cost of others'.
The natural Kechari Mudra is, if one can say so, unconditional, it flows from or goes hand-in-hand with unconditional love. The forced version is more masturbative. ("Not that there is anything wrong with that!" ~ Seinfeld)

When the Kechari Mudra is brought about naturally, there are no dangers. So far I know of four people, including myself, who have experienced the Kechari Mudra in this natural way. I believe that there must be quite a number of people who could be ready for this***.

After Kechari Mudra experiences, which may happen just once or more often (there is no great significance as to the quantity of occurrences), bliss eventually becomes irreversible, as a physical change is taking place in the integrated human being.

The Kechari Mudra and Samadhi

Part of the dynamic of the Kechari Mudra is that the spine, pelvis and shoulders will curve and move differently, almost always in a gentle curvy/wavy motion, and one's muscles and nerves seem to be breathing. The nerves feel very vibrant and 'candy-taste' like.
Sexual intercourse may be less sought after or, if one wants to maintain it, it will take on an enhanced functionality leading into the various different levels of samadhi with... one's partner.

By the way, samadhi states can of course also be brought about by practicing advanced meditation, yoga and tantric techniques. I suppose what we have here is a total integrated human/divine love, at once from the most gross and physical to the most subtle and spiritual realities.

The Human Aura, the Kechari Mudra and the Uddiyana Bandha

The aura (the subtle energy field that surrounds the human body) is very much affected by the effects Kechari Mudra, as 'blobs' (so to speak) of the auric energy field part themselves off like parts of a flame, (similar to how flames can part themselves off from a burning fire) and are emanated into subtle energetic realms of possibly higher dimensional extensions. In myself this creates a sensation as though angelic or soul-like entities are produced. If that sounds far-fetched, just bear with me. Traditional Hatha Yoga literature (all too often unfortunately poorly translated and understood) I believe, describes this when it deals with the Uddiyana Bandha (Hatha Yoga Pradipika chapter III, sloka 54-59). In Tibet there were monasteries specializing in the 'creation of souls' through these techniques.
(If I won't be ridiculed I will write more about this, but it is possibly a sensitive issue to some. Hint! It has to do with the conception of children, the embodied soul or 'en-souled body', the male and female role in the conception of a human being. There is more to the sperm and the ovum than meets the eye!!!)

Kechari Mudra and Nectar, Soma or Amrita

Something else that can result from the Kechari Mudra experience (but this can be effected by different dynamics as well) is the production and flow of nectar (soma, amrita, ambrosia, elixir) in the oral/nasal cavities.

There is very little physical separation between the third ventricle in the brain and the space (akasha) below it. In fact, when there is enough cerebro-spinal-fluid (CSF) pressure built up in the spinal canal, the meninges and the other ventricles (by the way, these ventricles are not the same as the nasal cavities) some of this CSF will eventually drip through an aperture from the third ventricle into the back of the mouth cavity often onto the back of the tongue that, and when swallowed, it produces a sense of sweetness.





An animated view of the flow of bliss
This flow is related to Cerebro-Spinal Fluid or Amrita.
Source: http://www.healtouch.com/csft/csf.html





This liquid sweetness is called soma, amrita, ambrosia, nectar, elixir, food of the gods, etc.
Not everybody though who experiences this sweetness, senses the nectar drop, those who do experience a light drip of a phlegm like liquid substance. (It is often mistakenly diagnosed as a post-nasal drip or just phlegm without cold symptoms.)
The nectar flow usually results from a perfectly well aligned spine, when the hips, pelvis, shoulders and shoulder blades are moving, undulating and rotating unhindered and... a healthy, very loving life.
(In my experience and that of three other people I know (one female), sexual fluids take on a different role in the functioning of the male and female body.)