I know this feeling SO well. For me, it is the precursor to dp. Even trying now to discuss it or explain it, I have a million ideas come into my head that I can't seem to sort out, like I'm not sure what the important bits are and whats not. Affects my essay writing and getting anything done at work. I make lists but find it hard to accomplish anything. I've always thought it's a bit like ADD.
Basically, as soon as my thoughts get a bit out of sync or feel odd, instead of just GETTING ON WITH AND FOCUSING OUTWARD, I try frantically to regain control, inside my head. Instead of just carrying on with life, which would be much more productive.
The frantic search for control, ie lists of thoughts, things to do, etc are not the answer but it is VERY addictive to try and follow each train of thought or try not to forget something 'important' or that other thought which conflicted with what you perceived as a realistic point of view. It does this because you are too introspected and focusing too much on the thoughts.
Think of it like this (I kind of came to this conclusion after pestering Janine with queries on this exact subject and reading a few books) -
It is so counterproductive to try and think your wait out of a confused state. No matter how hard you want to fight for control of your mind, let go. Go back to doing what you were doing, instead of thinking about what you were doing. Then you will gain perspective, a normal healthy realistic relationship with the way your perceive the world. Then you will not have conflicting ideas about which thoughts are important or not etc because you will see they are actually just thoughts, not anything in the real world, and you will be able to take them or leave them. Yep, Im not making much sense either, because the more I try and focus on this subject, the less clear it becomes.
You will be able to think clearer on any subject that needs addressing when your brain is working better! And the chances are those things wont seem half as important as they do now, because you will be much more interested in living in the real world as opposed to your head.
Obsessive thoughts are a way of trying to control something which you can't control in that manner. Once you see how counterproductive it is, it is much easier to say STOP! And then continue your life.
I had so much to do that I spent all weekend worrying about it, thinking about it to the extent where it became impossible to think straight about what was important and what wasn't. My unrealsitic point of view disabled my brain. This morning, I awoke, got up, no procrastination, just got on with what I had to do. I am not thinking, I am doing, and I feel a hundred times better for it. However, making this post is a slight contradiction to that so I am going now to get on with my work!