We report the case of a man who had an 11 year history of the delusional idea that he was transparent ("like a piece of glass"), associated with alcohol abuse. The intense fear he experienced when people seemed able to look right through him caused him to hurry along the streets, seeking shadows or darkness in order to hide his face as far as possible. He discovered that alcohol suppressed these symptoms and therefore, during episodes when his delusion was most manifest, he drank heavily.
Update: False alarm. Further down in the case: "He was never financially embarrassed, took pride in his independence and had built his own house." No way we're related.
(Case report from the very interesting Priory.com, a compendium of online medical journals, one of which, the impressively named International Journal of Veterinary Medicine, currently has an article on canine Chronic Fatigue Syndrome.)