Overthinking. It's something we all do at times – so many of us that it cannot really be said that it is automatically related to mental illness. But in some cases, it is a symptom.

Let's start with depression, a subject about which I know a thing or two. When I was in a depressive phase of my (undiagnosed) bipolar disorder, I could, as the saying goes, overthink a ham sandwich (once I actually overthought a BLT). When I was depressed and/or anxious, it seemed as though I had a recorder in my head that would play back for me every stupid thing I had ever done – even such a small thing as handing the wrong person a glass of water. At random moments, the memory would pop up, usually with full color and sound, and I would again castigate myself for being so stupid.

I agonized over decisions. Should I call a friend to tell him or her about a phone call I received that might affect them? One time it was the right thing to do, with positive consequences. Another time it was also the right thing to do, but with negative consequences. Dilemmas like that made it even more difficult to know what to do. Indecision paralyzed me. When I couldn't figure out the consequences ahead of time, I couldn't know if my decision was correct. Of course, this is true of most people and many decisions, but the dilemma would derail my thoughts and leave me vacillating.

Intrusive thoughts are quite often symptoms of depression and bipolar disorder, and they can be valid or nonsensical. Are my children getting an appropriate religious education? Where is my passport (when no trip is remotely planned)? They can keep one awake at night.

Psychologically speaking, overthinking and intrusive thoughts are definitely symptoms of OCD. Did I lock the door? Better check three times. Did I leave the stove on? Better check four times. Has the milk in the refrigerator expired? Did my cat get out the door when I wasn't looking? Better go out and look around. Will I throw up when I ask my boss for a raise? Better not try. Does my aching knee mean I'm getting arthritis? Should I call my doctor about it? Will he think I'm imagining it? My mother only loves me because she's my mother, not because of who I am. These kinds of thoughts can be disabling, crippling, or at the very least painful. They can cause you to doubt yourself and everything you do.

In mania, overthinking comes later. While you are spending or gambling or having risky sex or driving recklessly you don't question it. It's only later, when the episode wears off, that you have intrusive or obsessive thoughts. Oh, my God, why did I do that? How can I ever pay for all that? Are my finances so screwed up now that I can't pay my rent? Did I binge drink and hurt someone? I'm so ashamed. I feel so guilty.

Cognitive Behavioral Therapy (CBT) may be one way to confront your intrusive thoughts and push them aside in favor of more productive thinking. Talk therapy of the usual sort may help you develop coping mechanisms for when your thoughts run away with you. And psychotropic medication may lessen or eliminate the underlying problem that causes you to have intrusive or obsessive thoughts. In my case, it was the latter two. I still get stymied by some decisions, but I don't lie awake and think about them. I discuss them with someone else (my husband, my therapist) to get feedback. Then I make a decision and stick with it, or move on to thinking about something else.