Nancy School - 
Early French school of psychotherapy founded in 1866 by A. A. Liebeault (in the city of Nancy). Hypnosis played a great part in the treatment methodology and much research was conducted into this subject, particularly by H. M. Bernhiem.
Necrophobia -
Abnormal fear of death.
Negative Hallucination -
Not seeing something that is actually there. Often used in stage hypnosis.
Negativism -
A form of resistance to suggestions. Can be so strong that the opposite course of action to the one suggested is taken, (active negativism). Simply refusing to accept suggestions is termed 'passive negativism'.
Nervous Sleep -
The term coined by J.Braid to describe hypnosis.
Neurodermatitis -
Skin inflammations that have a psychogenic causation. 
Neurosis -
A functional problem of entirely psychogenic origin, often manifesting as maladaptive habit/s. Usually treatable by hypnotherapy.
Nightmare -
A dream that arouses great fear and alarm. 
Noctambulism -
Sleepwalking.
Nocturnal Enuresis -
Involuntary urination at night. Bedwetting. Common in children up to 4-5 years of age and is usually grown out of. Treatable with hypnosis after this time.
Nosophobia - 
Excessive fear of disease.
Nyctophobia - 
Irrational fear of the night, or darkness.