Alan always has been terrified of spiders. he refuses to enter his bedroom at night until it has been thoroughly checked for spiders. even a picture of a spider makes him extremely uncomfortable. most likely, alan is suffering from a psychological disorder called

specific phobia

Explanation:

A specific phobia refers to an irrational fear and anxiousness that someone possesses when it comes to particular objects or situations.

This fear causes the person to avoid anything that is associated with that object such that they may get anxious even when the object is mentioned or shown to them in a picture like Alan he is anxious even at the picture of spiders.