Take a walk, alone.
You would be amazed at where your mind goes when your feet are going somewhere. Leave your house and walk about a mile. Then turn around and come back. Don't make any stops along the way, no exact destination or purpose other than to walk. This is not the time to pick up milk or drop off letters in a mailbox. You do not want to be thinking about those things on your walk.
Sometimes when the mind is in a fog of some sort, doing something physical that doesn't require much thinking can set it free. The extra oxygen is good for your brain, too. And the exercise will release endorphins that will improve your mood.
When you come back, you'll be ready to work again, often with fresh ideas you didn't have when you left.
If the weather is bad, then find another repetitive physical activity that doesn't require much thought, like sweeping the floor, washing dishes, scrubbing your tub, etc.
While there are some people that do use these kinds of activities like mouser said, to procrastinate, often when done because your brain is stuck (rather than to avoid a task), it can help fix things and make you more productive instead of less.