Physical pain will do it. Exercise is one option, but for me it always seems to be the bad "I am destroying my joints" kind of pain so I stop before it hurts enough to reset my thought patterns. Holding a mug of tea that's almost but not quite hot enough to burn, and concentrating on that feeling to the exclusion of everything else, seems to work decently. A properly forceful backrub is better, though it requires a partner. And if your partner is a sadist then you begin to have many excellent options.