Sleep Terror Disorder
Sleep Terror Disorder (also known as Night Terror Disorder)
is the second Parasomnia described by
the psychiatrist's bible, the DSM-IV.
The most important criterion for this disorder is the repeated occurrence
of sleep terrors, which are screaming, crying, and/or jerking movements
such as lunging forward while still asleep. These symptoms can also overlap
with those of somnambulism (sleepwalking); that is, a person suffereing
a sleep terror (screaming, crying, etc.) may also be quite mobile, going
through all the motions of being attacked by some horrible monster, and
yet be fully asleep. 
A person suffering a sleep terror is asleep,
and as such is generally unaware of his or her environment (familiar walls,
doors, etc. may prove no hinderance, as with other forms of sleepwaking,
but family memebers and friends are rarely able to contact the sufferer).
Sleep terrors can suddenly transition from sleep to waking (though they
may not); in such cases, the sufferer generally reports feelings of intense
fear, though what they fear they are unable to describe, nor do they
recall the events of the sleep terror. According to the DSM, in order to
classify sleep terrors as a disorder, a particular sufferer must experience
significant impairment in personal, occupational or social functioning as
a result of the symptoms; however, family or friends will often seek treatment
for a sufferer because they (the family members) are losing sleep due to
the nightly screaming and crying. Sleep Terror Disorder occurs most often
in preadolescent boys, although, as with most disorders, anyone can have
it.
For people who would like a bit more detail, check out:
For even more info, you might want to peruse this helpful
site:
http://www.iowaclinic.com/515-241-5785/iowa_clinic/adam/view_document/
health_illustrated_encyclopedia/1/000809.htm