Jokers Purple Rain

I've heard that Jack Nickles stated that playing a character as complex as The Joker take a lot out of you. If you're not a trained method actor it can cause you a lot of stress. I can't confirm this, nor do I feel like Googling the quote. Lets just say its a possible truth. Is this the reason why Ledger was so restless playing the character?

Leto was said to have acted strangle, when getting in the mind of The Joker, playing practical jokes on the cast. Mark Hamill has voiced Joker more than anyone ever will. His voice is unanimous with the devil in purple. I believe that Hamill understand the spirit of Mr. J. and that spirit is pleased with his work. 

But the spirit gets hungry, claiming the lives of the ones we least expect first ledger now Prince. Many people forget that Prince played the Joker while writing the soundtrack to the Batman Movie (1989). this happens the same year the Killing Joke comes to home video. There is no evidence to back up any of these statements, only rumors and speculations.