concerning the white light and tunnel,
I agree with Bennie on this one. During a crisis situation your body will do everything it can to get itself back to functioning. [Examples: coughing and throwing up water for near drowning, shivering for near freezing, adrenelin and endorphin release for extreme pain, retention of water volume to fight against blood loss, etc] In the same way, if the brain is in a process of shutting down it will give itself an electrical shock, similiar to a defibulator, to wake itself up and as a side effect of this causes a "white light"

Now the following is my own theory, in the same way the body works itself over, the mind is also busy fighting against death. Since it does not have the ability to actively "fight" it uses imagery to strengthen the resolve of the conscious mind to live. Some ways of doing this could be by calming the consciousness in darkness, (back to the womb?) provide images from the person's mind of loved ones or close friends, even possibly creating dialogue, or created images of people who would calm or strengthen us (who could possible feel in danger when sitting before you is a grandmotherly woman smiling and offering you a cookie, or a man with the appearance of a saint?)

Arcoss