if it's painful have you considered it could be physical? felt something like that couple of times, it could be nerves been crushed in the spine.
Thanks but no it was not painful, and only happened just as the images were registering in my brain. After that I got up & had no ill effects. I should have mentioned it was somewhere in the lumbar region, where I don't tend to have back problems. Anyway it was not musculo-skeletal - more like a spark. Hasn't come back since.
In fact my OBEs have come to a stop too, which is disappointing. I'm wondering if it's the season. I'd had these spontaneous "hallucinations" for about 5 years (and generally viewed them as a nuisance), but only in 2011 did I realize what was happening. I had a few nifty projections - but they've all but gone now, and I don't know why.
So I was happy to see even a brief image, happy to get a strange sensation too. For what it's worth, I think these images in the half-awake state are a form of remote viewing. The tricky part is keeping your mind and thoughts out of it. As soon as I start to think, the image vanishes.