Sometimes at night when I'm in bed with my eyes closed waiting to fall
asleep, a quick flash of white light appears in my field of vision. 
It's kind of like a camera flash, but not quite as silvery.  This
flash usually occurs in response to a single "click" sound I hear
(often from the inside of the computer monitor as it cools down). 
What is the medical explanation for this?

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Clarification of Question by kariny-ga on 29 Dec 2002 18:08 PST

By the way, I am in my mid-20s and have mild nearsightedness (-2.25, -1.00).

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Request for Question Clarification by digsalot-ga on 29 Dec 2002 19:26 PST

Do you mean the click sound is coming from the computer or do you mean
a click sound similar to a cooling monitor accompanies the flash but
originates in your head?

Hi there

Well, I decided to go ahead and answer regardless of where the click
is coming from.  You may just be having a "Myoclonic jerk."  And as
far as the noise is concerned, if it is coming from inside your head
you may just be experiencing "exploding head syndrom."  You may be
doing them both at the same time.

Now exploding heads and strange jerks may seem a little frightening at
first but they are usually nothing to worry about.  They are mostly
just "sleep surprises."

Atually, my exploding head has nothing to do with sleep.  It usually
follows a night on the town and is often found in the company of flies
stomping across the ceiling or snowflakes crashing on the roof.

However, I don't think that is what you are talking about.

As for your light flashes and clicks (if they are coming from inside
your head), I don't think anybody has a clue.  However, there are
theories, since theories rush in where angels fear to tread.  Sort of
like answering this question.

Jerks and flashes and having your head explode are of no medical
significance.  At least that is what the experts say.  It's completely
normal.

There are various kinds of "sleep starts."  One is an "auditory sleep
start," sometimes called an exploding head.  As you fall asleep,
instead of jumping awake with a twitch, you wake to a snap, click or
cracking sound that seems to originate in the center of your own
noggin.  Sometimes the sound can seem as loud as a gun being fired
next to your ear or it can be a simple click.

Another 'sleep start' is a "visual sleep start."  It can take place
alone or in conjunction with an auditory sleep start.  A visual sleep
start is a flash of white light that seems to originate within your
head or behind your eyes.  Such a flash may be triggered by an outside
stimulus such as your computer monitor click or the click may
originate with you.

And of course, there is the Myoclonic jerk itself.  That is when you
awaken with a twitch or jump.  This often accompanies the sensation of
falling as you are about to drop off.  Some people may have experience
with all three.  Hopefully, not all at the same time.

The various theories are related in that these jerks, explosions,
flashes and twitches are a natural step in the body's transition from
alertness to sleep. As we drift off, our bodies goes through some
physiological changes to prepare for a few hours of dreamtime. Our
breathing rates change.  Our temperature may change. And our muscle
tone changes, too.  These sensations, the theories go, may be part of
that transition.

Now if you are also a sleep walker, you have a great conversational
ice breaker at social gatherings.  You can tell people you are a
myoclonic jerker and a complete somnambule as well.  Let them think
you are working on a secret government project.

The following websites were used to compose the answer:

"Night Terror Resource Center"
http://www.nightterrors.org/parasomnia.html - Sleep starts are about
three fourths way down the page.

"Sleep and common sleep disorders"
http://www.betterhealth.vic.gov.au/bhcv2/bhcArticles.nsf/(Pages)/Sleep_and_common_sleep_disorders?OpenDocument
- From Better Health channel

"Noises in the head are scary but harmless"
http://www.freep.com/news/health/good24_20001024.htm - From Detroit
Free Press

Search - google
Terms - "sleep starts"

If I may clarify anything before you rate the answer, please ask.

Cheers
digsalot

Glad to know that my vitreous is not slowly detatching from my retina!  Thanks!

kariny,

Something else to bear in mind is that, if you are sleep-deprived,
your brain can do some weird things. Once during midterms in college,
when I had been up for about 40 hours straight, I was watching a slide
show in a darkened lecture room. Suddenly all the lights in the room
came on (and I mean a really sudden, brilliant flash)! I looked
around, wondering why other people weren't getting upset at the person
who had turned on the lights. Then the room faded to dark again, and I
realized that the lights hadn't come on at all, I had had some kind of
"vision".

I was alarmed enough to do some research, and I discovered that if you
are sleep-deprived, you can see sudden flashes of light, or auras,
which are presumably the result of your brain rebelling at the abuse
of not getting enough sleep. I recently had another of these
experiences after an all-night session of "Google-Answering". So your
flashes might be your brain's way of telling you to get some shut-eye.

Regards,

aceresearcher

I've noticed this phenomenon too, and it's definitely not from imagined clicks.

A lighting fixture in my living room has the annoying habit of
clicking about a half hour after it's been turned off whenever it has
been on for a long time (probably because the light bulb heats it up,
and when it cools down, it contracts, which will make it click). It
does this consistently. And frequently, when it makes that click, I
will see a flash. I know I'm not imagining the click because it's
fairly predictable, and because on multiple occasions I have confirmed
with my wife that she heard it too. This only seems to happen when I'm
in light sleep.

I would also be interested in learning more about what causes the
flash in response to actual external stimuli.

Okey, so here's the deal: kariny-ga, My friend and I experienced the
exactly same thing, about the flashing white light in the middle of
the night, with our eyes closed, at the exact same time. The light
lasted for less than half a second, and were extremely bright. It was
so amazingly bright, that no camera flash could have same effect with
the eyes closed. And with the sound! Like a hallow sound, like a very
bright lamp-sound get when turned off...Ok blablabla "Myoclonic jerk."
thingy, but at the same time with two people! It frightened us both..
HELP!

I am experiencing exactly the same flashes as kariny-ga and drip-ga.
Clicks are real, usually very weak. My flahes are usually red, white
or mix of both.
They started a year ago with my illness (a long illness that requires
heavy treatments), a neurological illness.