i used to have the same problem myself and im nearly 27 now and am still not fond of the dark,,but i have come to realise that it was/is an irrational fear,, a night light may help, my mum had to leave the landing light on and leave my door open,, i also found when my little one got scared of doctor who it helped him showing him doctor who confidential after so he could see how it was made and the people in the costums,, maybe you can find out if there is any behind the scene footage of the film that scared your son ..
My son is just gone 11 and is acting the same way. He won`t go upstairs alone or sleep alone. It`s getting out of hand. In other peoples houses he wont go to the bathroom alone. Most people i speak to say he will grow out of it but to me it seems to be getting worse. Any advise. Thankyou. Gert.