Dead Pixel?

Keep an eye on it (no pun intended), it's not "dead" but possibly defective.

If this is a one time thing, I wouldn't worry. If it keeps happening occasionally at the same spot, I'd run dead pixel buddy (do a search for it) to see if it's not the graphics card/drivers.

A simple explaination of the transistors that control LCD pixels (How Stuff Works.com - I love that site!)

Each pixel has three transistors behind it, each controling a color (R,B,G). (They used to be wired to the edge of the panel, along the top and bottom, each edge controlling half the screen. That's why the screen would always load in horizontal sections.)
If none are getting juice, then the pixel is "dead", which I think results in a black pixel all of the time.
One of the transistors can be shot, resulting in a dark pixel that you only notice on light backgrounds.
Of course, 2 transistors could be shot, resulting in maybe a darker pixel? (I dunno)
In any case, these can be tolerable.
But here's the rub- You could have a "defective" (not actually dead)transistor that allows too much voltage to the pixel, causing a "hot", or bright pixel.
This is what it sounds like you have, and it's more annoying than a dead one because it usually sticks out like a sore thumb no matter what the background color is.

I don't know what the deal with it going away is, though. Maybe the screen refreshing gives the transistor the opportunity to shut it down completely till it cools off?
Check to see if it's darker than the rest when it isn't bright.

I would send it back after ruling out the suggested test of the GPU. If it's a hot pixel, it may take a long time to burn itself out and become dark, and therefore more tolerable.

try using the pencil eraser method, by gently pressing on that spot

I've seen tons of dead pixels and most are only visible on dark background. Whites are perfectly whites most of the time.

Not specially disturbing considering that lot of program and web pages use white backgrounds.