The conch is the symbol of the spiritual call.
The conch is the call to realisation.
The conch is perhaps the proclamation of victory.
The experience you had was simply the descent of the Divine Force into the body. By your attitude and aspiration you called for it to work in you, so it came. Such a descent brings naturally a deep inward condition and a silence of the mind, and it may bring much more — peace, a sense of liberation, happiness, Ananda. It is very often attended as in this experience by a light or luminosity. It was felt enveloping the upper part of the body down to the cardiac centre, because it is these centres, the head and heart centres that are first invaded and occupied by whatever descends from above, Consciousness, Force, Light or Ananda. Usually, there is at first a pressure from above on the head and then the whole head is occupied, as you feel now with the "fourmillement" at the time of concentration. Once the head with its mental centres is open and occupied, the Force descends rapidly to the heart centre, unless there is some obstacle or a resistance in the higher vital parts. From there it sends its stream into the whole body and begins to occupy the vital and physical centres - from the navel to the Muladhara. The coming of this experience, occupation of the body, by the Force from above, is a great step forward in the sadhana.
He who now stares at the world with ignorant eyes
Hardly from the Inconscient's night aroused,
That look at images and not at Truth
Can fill those orbs with an immortal's sight.
Yet shall the godhead grow within your hearts,
You shall awake into the spirit's air
And feel the breaking walls of mortal mind
And hear the message which left life's heart dumb
And look through Nature with sun-gazing lids
And blow your conch-shells at the Eternal's gate.