This issue started happening after I updated to OSX Mavericks.
I have an external monitor connected to my Macbook Pro (2010), and everything works just fine and dandy.. until my Mac doesn't have any activity for a bit and turns off the screen (NOTE: not the whole Mac is asleep at that point, it's just the screen).
Then when I swoop around on my trackpad to wake it back up, it won't recognise the external monitor the way it used to. Suddenly the arrangement is flipped (i.e. it's now below my Mac rather than above it), and the resolution is switched to 800x600 rather than the normal 1680x1050.
When I then pull the plug and plug it back in (while my Mac and its screen are wide awake), it finds its old configs again and fixes the resolution and arrangement.
Has anyone experienced anything similar, or is there a fix available? Or should I just consider this an unresolved bug, report it to Apple and hope for the best?