one of Steve's old blog posts describe a technique where you sit down and do what you're supposed to for at least 30 minutes. After 30 minutes you are free to do what you want.
He calls it timeboxing
Overcoming Procrastination by Steve Pavlina
"No matter how unpleasant the task, there's virtually nothing you can't endure for just 30 minutes if you have a big enough reward waiting for you."
Well, I think the most basic reward is peace of mind. The only way to get work out of your head is by getting something done. If you have a time box of 30 minutes, you know that the workload is very limited so you can get through it. Afterwards you can feel good about having done something.