The sun is the symbol of Divine Truth, it stands universally for the supramental Light, the divine Gnosis. Light is the light of Consciousness, Truth, Knowledge -- the sun is the concentration or source of the Light. It is the symbol and power of the inner or higher Truth; to see it in meditation is a good sign. The Sun symbol, for instance, is usually dynamic.
What you saw was indeed a sun, the sun of blue light which is the light of a
higher mind than the ordinary human mind. This higher spiritual Mind is trying to wake in you, but at the beginning
there is always a difficulty because the consciousness is not habituated to receive, so there is the sense of pressure
deepening sometimes into a feeling of headache or this feeling of the head preparing to split. It is nothing but
a sensation in the physical created by the inner mind trying to open under the touch from above.
In the Upanishad the sun is the symbol of the supramental Truth and it is said that those who pass into it may return but those who pass through the gates of the sun itself do not; possibly this means that an ascent into the supermind itself above the golden lid of overmind was the definitive liberation.