So, what actually is werewolf or lycanthropy? Is it a fact based on concrete evidences? Is it a myth, fabrication of feeble minds? Is it an exaggeration of some other things? Well, all these questions have been puzzling mankind for last 5 centuries. Though many ingenious hypotheses have been suggested as possible explanations, definite conclusion can't be drawn. Some experts have tried to observe it as purely supernatural phenomena while others have relied on scientific observations. Contradictions and debates still persist and will continue till any single theory solves the jigsaw which seems unlikely considering complexity and diversity of the topic.
Some people during middle ages believed that the werewolf was the projection of a demon, which made its victims appear as a wolf in his own eyes and to those around him. For others, the werewolf was a direct manifestation of the Devil. Early seventeenth century French author Henri Bouguet believed, as did a great many people of that day, that Satan would leave the lycanthrope asleep behind a bush, go forth as a wolf, and perform whatever evil might be in that person’s mind. According to Bouguet, the Devil could confuse the sleeper’s imagination to such an extent “that he believes he had really been a wolf and had run about and killed men and beasts.”
Robert Burton, the clergyman and scholar, considered lycanthrope to be a form of madness as mentioned in his book Anatomy of Melancholy in 1621; he blamed every thing from sorcerers and witches to poor diet, bad air, sleeplessness and even lack of exercise for this.
The Mysteries of Magic, written by nineteenth century French occultist Éliphas Lévi, postulates the existence of phantom - a body that acts as mediator between a living organism and the soul. “Thus in case of a man whose instinct is savage and sanguinary, his phantom will wander around in lupine form, whilst he sleeps painfully at home, dreaming he is a veritable wolf.” Lévi believed that the wounds so often reported in the cases of werewolves could be attributed to the out-of-body experience. He saw the human body as a subject to magnetic and nervous influences and capable of receiving the wounds suffered by the metamorphosed shape.
Contrary to the popular explanations existed during middle ages, few doctors at that time asserted that it was caused by an excess of melancholy or an imbalance in humors, the liquid or fluid part of the body. Many doctors believed that such melancholy could lead to insanity and delusion. One physician recommended that the lycanthrope should be treated with baths, purging, bleeding, dietary measures and rubbing opium into the nostrils.
Taken from here, It also tells of the other condition that was mentioned above.
http://members.tripod.com/alam25/exp.htm
