I was looking up something in Professor Sonja Lyubomirsky's excellent book, The How of Happiness, and I came across an interesting passage. (I'd marked it, so clearly I'd read it before, but I didn't remember it well.)
Many of us believe that when we feel down, we should try to focus inwardly and evaluate our feelings and our situation in order to attain self-insight and find solutions that might ultimately resolve our problems and relieve unhappiness. Susan Nolen-Hoeksema, I, and others have compiled a great deal of evidence challenging this assumption. Numerous studies over the past two decades have shown that to the contrary, overthinking ushers in a host of adverse consequences: It sustains or worsens sadness, fosters negatively biased thinking, impairs a person’s ability to solve problems, saps motivation, and interferes with concentration and initiative. Moreover, although people have a strong sense that they are gaining insight into themselves and their problems during their ruminations, this is rarely the case. What they do gain is a distorted, pessimistic perspective on their lives.
One of the tensions within happiness -- at least for me -- is the tension between constructive attempts at greater self-knowledge and pointless rumination. Once I started paying more attention to my habits of thinking, I began to do a better job of refraining from overthinking. When I find myself thinking in circles, I find an area of refuge, say, or I re-read one of my favorite works of children's literature -- my favorite emotional comfort food. Or, if it's nightime, I go to bed early. Things really do look better after a good night's sleep, and often something that had me agitated the night before seems much less worrisome the next morning.