Nyctophobia is fear of the dark. It is a common fear or phobia among children and, to a varying degree, of adults. Fear of the dark is usually not fear of darkness itself, but 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 nyctophobia seldom appears before the age of 2. Nyctophobia comes from the Greek νυκτός (nyktos), genitive of νύξ (nyx), "night" and φόβος (phobos), "fear". Other terms for the phobia are achluophobia, scotophobia (from σκότος - "darkness"), or lygophobia (from λυγή - "twilight").

The unnatural fear is commonly caused by negative experiences, like getting scared in the dark or even by watching ghost and horror films where darkness is often portrayed.

Sufferers may have symptoms including dizziness, trembling, fast heartrate, shortness of breath, and panic attack.

A popular and effective treatment for the fear of darkness is cognitive-behavioral therapy, specifically exposure therapy. Medications and self-help methods may be necessary to cope with the worst symptoms.

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