Somnambulism

Somnambulism (pronounced som-nam-byuh-liz-uhm or suhm- nam-byuh-liz-uhm)

Sleepwalking; a condition characterized by walking while asleep or in a hypnotic trance

1786: A Modern English borrowing, via the French somnambulisme from the New Latin somnambulismus (sleepwalker), the construct of the original being somn(us) (sleep) + ambul(āre) (to walk) + -ismus (equivalent to the English –ism).  In English, the construct became somnus + ambulo +‎ -ism.  Somnus came from the Proto-Italic swepnos, from the primitive Indo-European swépnos, from the root swep- (to sleep); the form spread east too, including the Lithuanian sãpnas.  Ambulo is from ambi- +‎ alō (to wander”), from the primitive Indo-European hzel- (to wander) and was cognate with the Ancient Greek ἄλη (álē) (wandering) & ἀλύω (alúō) (to wander in mind, to roam).  The suffix –ism is ultimately from either the Ancient Greek -ισμός (-ismós), a suffix that forms abstract nouns of action, state, condition, doctrine; from stem of verbs in -ίζειν (-ízein) (from which whence English gained -ize), or from the related suffix from Ancient Greek -ισμα (-isma), which more specifically expressed a finished act or thing done.  Somnambulist is a noun, somnambulation a verb and somnambulistic an adjective; in the technical jargon of clinicians, there’s the mysterious semisomnambulistic, the implication presumably that somnambulism (at least when not raised in court as a defense) may be a spectrum condition.  Somnambulism, somnambulator, somnambulation, somnambulance & somnambulist are nouns, somnambulate & somnambulating are verb, somnambular, somnambulic & somnambulistic are adjectives and somnambulistically is an adverb; the most common noun plural is somnambulists.

Sleepwalking scene, Lady Macbeth (1829), by Johann Heinrich Ramberg (1763–1840).

As it was in science, philosophy and art, the Enlightenment proved productive in words, creations needed to describe newly discovered things and novel ideas.  The noun somnambulism came into use originally during the excitement over "animal magnetism"; it won out over noctambulation which endured not long.  A flurry of linguistic action ensued in the early nineteenth century including somnambule (1837), somnambulator (1803), somnambulary (1827) & somnambular (1820).  When the theory of animal magnetism (the doctrine that one person can exercise influence over the will and nervous system of another and produce certain phenomena by virtue of a supposed emanation called animal magnetism) was published in 1778, it created great interest.  Called mesmerism (from the French mesmérisme and named for Franz Anton Mesmer (1734-1815), an Austrian physician who developed a theory of animal magnetism and a mysterious body fluid which allows one person to hypnotize another), the still used word is synonymous with hypnotism or artificial somnambulism.  Another similar word for the same effect was braidism, named after English physician James Braid (1795-1860) and an ancient term for "hypnotic suggestion" was "mesmeric promise".

Somnambulism is classified among the parasomnias, sleep-wake disorders characterized by undesirable motor, verbal, or experiential phenomena occurring in association with sleep, specific stages of sleep, or sleep-awake transition phases.  In the fifth edition of the American Psychiatric Association's (APA) Diagnostic and Statistical Manual of Mental Disorders (DSM-5 (2013)), somnambulism is noted as a condition rather than a mental illness with most attention given to the protocols to be followed when awakening sleepwalkers.

Lindsay Lohan and her lawyer in court, Los Angeles, December 2011.

The other profession to take interest in somnambulism is the criminal bar.  At common law, sleepwalking can in some circumstances be a complete defense to any charge including murder.  That’s because the law (generally) will convict in criminal matters only if intent can be proved and that requires a “guilty mind”.  The legal Latin is mēns rea (literally “guilty mind”), from the English common law precept actus non facit reum nisi mens rea sit (the act does not make a person guilty unless the mind is also guilty).  It’s rarely successful but if it can be proved a defendant was, at the time of the act, “a sane automaton” (ie in effect sleepwalking and thus unaware of their actions), it’s an absolute defense.  Lawyers like it because sane automatism is a defense even against crimes of strict liability like dangerous driving, where no intent is necessary.  If the defense succeeds, the defendant walks free, unlike a finding of insanity (ie the notion of the insane automaton) where even if not found guilty, they're anyway locked-up.