Body Double

Jake Scully (Craig Wasson) is a struggling actor who has lost his role as a vampire in a low-budget horror movie after his claustrophobia thwarts shooting. After returning home to discover his girlfriend cheating on him, he is left without a place to stay. At a method acting class he meets Sam (Gregg Henry) who closely monitors Scully's revelation of his fears and the childhood cause of his claustrophobia. They go to a bar where Scully is offered a place to stay; Sam's friend has left town temporarily and needs a house-sitter for his ultra-modern home in the Hollywood Hills.
During the tour of the house with Scully, Sam is especially ecstatic about one feature: a female neighbor, Gloria Revelle (Deborah Shelton), who erotically dances at a specific time each night. Sam has even set up a telescope which Scully cannot resist using voyeuristically to watch her. One night he sees Gloria being abused by a boyfriend. When she goes shopping the next day, Scully decides to follow her. Gloria makes calls to an unknown person promising to meet them. Scully also notices a disfigured "Indian," a man he had noticed watching Gloria a few days prior. Scully follows her to a seaside motel where apparently Gloria has been stood up by the person she was there to meet. On the beach the Indian suddenly snatches her purse. Scully tries to pursue him but in a nearby tunnel his claustrophobia restrains him and Gloria walks him out of it. They begin to impulsively and passionately kiss before she retreats. That night Scully is again watching through the telescope when the Indian returns. The man is seen breaking into Gloria's home. Scully races to save her but is attacked by Gloria's vicious dog. Gloria is brutally murdered by the Indian with a huge handheld drill.




Chemosphere, the ultramodern house used in Body Double
Scully is then left to alert the police, who assume it was simply a fumbled robbery. Detective McLean (Guy Boyd), however, becomes suspicious of him after finding a pair of Gloria's panties in his pocket. Although McLean doesn't arrest him, he coldly tells Scully that due to his voyeuristic behavior, as well as not alerting the police sooner, is what helped caused Gloria's murder. Unable to sleep, Scully watches a pornography channel on television when he observes that the actress on screen, Holly Body (Melanie Griffith), dances in exactly the same sensual way that he saw Gloria dance. Now suspicious of Holly, he pretends to be a porn producer hiring for a new film so that he can meet Holly. In the process, he even ends up acting in a hardcore film himself.
During his talk with Holly at the house, Scully learns she was hired by Sam to impersonate Gloria each night, dancing in the window, with Sam knowing Scully would watch her and later witness the real Gloria's murder. Holly is offended at the suggestion she was involved in a killing. After storming out, she is picked up by the Indian who knocks her unconscious and drives her away. Scully follows them to an aqueduct where the Indian is digging a grave. They fight, at which time he discovers that the Indian is actually Sam in heavy make-up. Scully was a scapegoat providing Sam, who was Gloria's abusive boyfriend, with an alibi during the murder. Scully is overpowered and is thrown into the grave. However, he overcomes his fear and climbs out as Sam is accidentally knocked into the aqueduct by his own dog, not Gloria's, where both perish.
During the end credits, Scully is shown having been recast in his previous role as a vampire. Holly is there watching, as an actress doing a nude scene is then replaced by a body double.

Question: What was the root cause of Jake's claustrophobia
Answer: Childhood