I am highly sceptical of the third eye.
I believe it is a myth, a story used to
explain something of an unexplainable
phenomenon.
As you were nearing sleep, is it possible what you saw was nothing more then HI.
The eye of any human joe or josaphine can see light on the scale of about 300nm to 400nm.
However, in rare cases (such as tetrachromats) that scale is extended either higher or lower so in the full spectrum humans (as a whole) have the capability of seeing anywhere from 200nm to almost 800nm in select population (mostly females).
With this broad range branching beyond so called visable light, we reach wavelengths that can pass through things as trivial as eyelids (the thinnest skin on the human body) with great ease, this may lead to the ability to “see” whilst your eyes are closed, or so called physcic xray vision.
there have been numerous projects researching peoples abilities to see light on the infared scale conducted by the united states army as well as a handful of medical institutes and universities.
I believe that the “third eye” is just another way of explaining this, and as light on either the ultraviolet or infared wavelengths is not normally registered or noticed due to the overwhelming input of “visible” light, when those wavelengths are blocked out, (such as in the dark, or when you have your eyes closed ) what you see is an unfamiliar spectrum that the brain neither knows how to fully procces nor understand.
C’est la Vie