Sen. Hillary Clinton blamed her collapse at a New York fundraiser on a stomach virus but Weekly World News has learned the shocking real reason she swooned and hit the deck -- the sexy thong panties Bill gave her for Christmas were WAY too tight and cut off the blood supply to her head! That's the word from highly-placed sources in the Clinton camp who say the former first lady "was just asking for trouble" when she didn't exchange the teeny-tiny red silk undies for a pair of he billowing white "granny panties" she normally wears.