how long does a marginated tortoise sleep for?

hi my name is kay. i have resently purchased an 8 year old marginated tortiose. we have changed her bedding and put some hey in there for her to sleep under, but it seems that she never comes out of there. she could sleep up to 24 hours without food or water. is this normal?? please let me know ASAP as i don't know whether to wake her up ???? thanks.