My cat sleeps in her litter tray?

My cat has been sleeping in her litter tray and i dont know why.i got her last week from battersea dogs & cats home.is this normal? is this dangerous to her health? how is it stopped?
Answer
Aww, is she sick? when i first adopted my little kitty he came home a little sick and was sleeping and hanging out in the litter tray. i took him to the vet, gave him medicine and when he was feeling better (and less nervous about his new home) he was not sleeping in his poop. :) def. get her checked out. anyone sleeping around their own feces is not nice !