Dear Zmuo,
Thank you for writing here. I assume that you are doing some research work on mudra and I quite appreciate your questions on mudras. Please do share your research if any on mudras and yoga.
As discussed earlier on your questions, every finger relates to one of the five element of the nature. The thumb relates to fire, the index finger to air (matter in gaseous form), the middle finger to ether (space), the ring finger to earth (solid matter), and the little finger to water (liquids) and the palm of the hand relates to the mind.
When mudras are formed by using thumb (fire element) to lightly stimulate one or more of the other elements as you touch the tip, nail, knuckle or base of a finger. So, we can stabilize, decrease or increase the influence of the linked element by joining the tip of corresponding finger, touching the back of the finger (nail or knuckle) or bring thumb to the base of the finger respectively.
You mentioned about Vata Nashak Mudra. We analyze in this way.
Vata is formed with air and ether and these correspond to index finger and middle finger. Vata being combination of air and ether, is dry, light, cold, rough, moving and always changing. Because of such nature, those who have predominantly vata dosha are mostly energetic, creative and lively. They are light sleepers with sensitive digestion. When vata gets out of balance, they can get anxious, have insomnia, lose weight and suffer from indigestion.
The position of fingers and thumb may be interpreted from the above principle on how an element is decreased, increased or stabilized. Mudra illustrated in this figure is meant to decrease the vata. When vata is decreased, it surely helps slows the movement not only physical but mental also and therefore improves the sleep.
But we should not forget that vata is not air but combination of air and ether.
In Gyan mudra, as illustrated in the 2nd figure, the tip of the index finger joins the thumb
. Index finger is indicative of air element and so, air is increased. This generates a burning desire for inner peace. This mudra is basically for calmness and helps one to tune to inner self because the mind enters the meditative state. So, this is not sleepiness but calmness of the mind as you have mentioned in your question.
So, coming back to your question, I think that there might have been misunderstanding of vata with the air and meditative state of mind with the sleepiness.
