Why do people conduct exorcisms?

ANSWER

In the 15 or 16 centery exorcism was quite common but many religions keep exorcism in the closet as a last resort cure if all medical practice for both physical and mental health then they turn to a witch doctor or priest and anyone else who has special authority..... BUT ALWAYS MAKE SURE THAT ALLL MEDICAL TESTS FAIL FIRST OR AN EXORCISM COULD BE THE DEATH OF THEM.