Computer issue: something's going on with my screen. Any ideas?

I’ll try my best to describe what’s going on. Please ask clarifying questions as needed! I haven’t taken screen shots of it, though that probably would have been helpful. I will next time it shows up, but I wanted to ask this question now and start getting ideas of what might be going on rather than wait.

My screen has started to do a thing where sometimes it “ghosts” previous images instead of moving cleanly on to the next thing. It would be like you reading this question on Fluther, and then trying to move to next question, only to find that you’re only seeing the next page at half opacity, and this page at half opacity, frozen and overlaying the active page.

This “ghosting” covers all of the screen except the first 1.5” along the top. That continues to work as normal.

It doesn’t seem to last too long. Eventually it will return to normal in a kind of fading/flickering way, though I will still see a dark/shadowy line on the left most side of what had been the border between the normal 1.5” of screen and 50/50 “ghostly” part.

Sometimes when I restart my computer to try and help the “ghosting” disappear, I will get a seemingly random-shaped patch or patches of the frozen image, at full opacity, covering parts of the screen—by “random-shaped” I mean it has an irregular, zigzag-y edge sort of like a country’s border. (Also, the shape isn’t quite the same each time it appears, though it often looks similar.) Usually the patches favor the left side, especially near where that dark/shadowy border can show up. My computer has a magnet in that area to hold a stylus on the edge of the screen. I’m not sure if that’s a coincidence or not.

Any guess as to what’s going on?