I think I also have this. When I have this thing, it is unbearable.
It is like you say, and I can't escape from it. I think at a thing without being able to stop myself. Only that in my case more ideas start to come about that thing, as if my imagination is overloaded, without being able to stop.
Also it also happened that I "hear" or sing a song in my mind and the same song never stops, it is similar to the first.
Sometimes if I lie down in my bed, for some period, this things start to dissapear.
I feel that my mind is stretched up and beyond to its limit.
I am also thinking that it is abnormal, I never had such things until I started to have POIS. I wonder if it has a name.