Have you ever been stressed all day because you can’t stop thinking of something unfair that happened that morning? Or the previous week? This human tendency to obsess, trying to work things out in one's mind, is common. When these thoughts turn more negative and brooding, that's known as rumination.

Rumination is comprised of two separate variables -- reflection and brooding. The reflection part of rumination can actually be somewhat helpful -- reflecting on a problem can lead you to a solution. Also, reflecting on certain events can help you process strong emotions associated with the issue. However, rumination in general, and brooding in particular, are associated with less proactive behavior and more of a negative mood. Co-rumination, where you rehash a situation with friends until you’ve talked it to death, also brings more stress to both parties once it passes the point of being constructive.

Rumination has several negative effects:
Stress. Studies show that rumination can raise your cortisol levels, signifying a physical response to stress.
Negative frame of mind. Not surprisingly, rumination is said to have a negative affect, or produce more depressed, unhappy mood.
Less proactive behavior. Research has shown that excessive rumination is associated with less proactive behavior, higher disengagement from problems, and an even more negative state of mind.
Self sabotage. These types of coping behavior can create more stress, perpetuating a negative and destructive cycle.
Hypertension. Rumination may prolong the stress response, which increases the negative impact of stress on the heart.