When tuning into the subtle “nudges” of the life force, as felt in the spine during meditation, you may find yourself naturally lifting/stretching the spine upwards…because it feels good to allow the expanding energies an unimpeded pathway to flow in the spine. You will then viscerally understand the recommendation of meditation technique to “keep the spine straight.”
However, what technique does not normally describe or suggest is how to feel into the infinitely subtle sensations that “nudge” the body to move/adjust/dance in nuanced micro-movements…while keeping the spine erect.
When deeply listening and feeling into the Life Force (Kundalini), in the beginning you may feel a growing sensation of “giddiness.” As you go slightly deeper, you will come to understand these sensations as a kind of “nudge” or “tap-on-the-shoulders” so-to-speak.
At that point you may intuitively relax and surrender to the lead of what is calling for your attention. You will then learn to enjoy the Cosmic Dance that the body and mind take up with the Life Force/Kundalini!
Also, the body will naturally assume certain postures, your hands/fingers will take up certain “mudras, all on their own, as you relax and surrender to the increasingly blissful inner sensations. These postures and mudras are spontaneous “shapes” and “geometries” that the body takes up as it falls into alignment/resonance with the Divine Vibration that moves through the energetic field of the body.