Duncan
Thanks for sharing your very personal experience.
" i remember feeling kinda disconnected, like i was there, but not quite there, and then i heard a noise, like white noise, like the noise from an old TV with the aerial out, the noise that accompanies "snow" on the TV."
What you describe is very much like the onset of the state of
"lucid dreaming". There are various ways you can go about practising to induce the state. I've achieved it half a dozen times in my life . Its usually been when I have been over- tired but not able to sleep. In full lucid dreaming state you are aware that you are dreaming and able to influence the dream if if it is your sub -concious doing the steering..you are essentially let loose in another world with some sort of personal control over the consequences.
Commonly you find yourself to have super human powers and the visual aspects is so real..the three dimensional reality is such that an encounter with something very frightening can effect you for days, much as a powerful dream can.
Many alien encounter stories ( involving interventions, probings etc), and `white tunnel' near death experiences are suspected by some psychologists to have been induced by rare stress induced release of Dymethyltryptamine which is a tryptamine neurotransmitter which occurs naturally in the brain, that can cause powerful hallucinations.