"Sociopathy is chiefly characterized by something wrong with the person's conscience. They either don't have one, it's full of holes like Swiss cheese, or they are somehow able to completely neutralize or negate any sense of conscience or future time perspective. Sociopaths only care about fulfilling their own needs and desires - selfishness and egocentricity to the extreme. Everything and everybody else is mentally twisted around in their minds as objects to be used in fulfilling their own needs and desires. They often believe they are doing something good for society, or at least nothing that bad. The term "sociopath" is frequently used by psychologists and sociologists alike in referring to persons whose unsocialized character is due primarily to parental failures (usually fatherlessness) rather than inherent features of temperament"
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http://faculty.ncwc.edu/toconnor/401/401lect16.htm
Chronic Depression also fits the bill;
"The group of symptoms which doctors and therapists use to diagnose
depression ("depressive symptoms"), which includes the important
proviso that the symptoms have manifested for more than a few weeks
and that they are interfering with normal life, are the result of an
alteration in brain chemistry. This alteration is similar to
temporary, normal variations in brain chemistry which can be
triggered by illness, stress, frustration, or grief, but it differs
in that it is self-sustaining and does not resolve itself upon
removal of such triggering events (if any such trigger can be found
at all, which is not always the case.)
Instead, the alteration continues, producing depressive symptoms and
through those symptoms, enormous new stresses on the person:
unhappiness, sleep disorders, lack of concentration, difficulty in
doing one's job, inability to care for one's physical and emotional
needs, strain on existing relationships with friends and family.
These new stresses may be sufficient to act as triggers for
continuing brain chemistry alteration, or they may simply prevent the
resolution of the difficulties which may have triggered the initial
alteration, or both."
There's many more.
And technically, there's no such thing as over thinking as every human is thinking every second of every day. There is such a thing as over pondering on a certain topic though.
