Noctiphobia

Fear of the dark is a common fear or phobia among children and, to a varying degree, adults.

Fear of the dark is usually not a fear of darkness itself, but a fear of possible or imagined dangers concealed by darkness. Some degree of fear of the dark is natural, especially as a phase of child development. Most observers report that fear of the dark seldom appears before the age of 2 years. When fear of the dark reaches a degree that is severe enough to be considered pathological, it is sometimes called scotophobia (from σκότος – "darkness"), or lygophobia (from λυγή – "twilight").

Some researchers, beginning with Sigmund Freud, consider the fear of the dark to be a manifestation of separation anxiety disorder.

An alternate theory was posited in the 1960s, when scientists conducted experiments in a search for molecules responsible for memory. In one experiment, rats, normally nocturnal animals, were conditioned to fear the dark and a substance called "scotophobin" was supposedly extracted from the rats' brains; this substance was claimed to be responsible for remembering this fear. These findings were subsequently debunked.

Nyctophobia is a phobia characterized by a severe fear of the dark. It is triggered by the brain’s disfigured perception of what would, or could happen when in a dark environment. It can also be temporarily triggered if the mind is unsteady or scared about recent events or ideas, or a partaking in content the brain considers a threat (examples could include indulging in horror content, witnessing vulgar actions, or having linked dark environments to prior events or ideas that disturb the mind). Normally, since humans are not nocturnal by nature, humans are usually a bit more cautious or alert at night than in the day, since the dark is a vastly different environment. Nyctophobia produces symptoms beyond the normal instinctive parameters, such as breathlessness, excessive sweating, nausea, dry mouth, feeling sick, shaking, heart palpitations, inability to speak or think clearly or sensation of detachment from reality and death.

Despite its pervasive nature, there has been a lack of etiological research on the subject. Nyctophobia is generally observed in children but, according to J. Adrian Williams’ article titled, "Indirect Hypnotic Therapy of Nyctophobia: A Case Report", many clinics with pediatric patients have a great chance of having adults who have nyctophobia. The same article states that “the phobia has been known to be extremely disruptive to adult patients and… incapacitating”.

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Wikipedia