I wouldn't recommend sleeping in the terminal. If you don't have enough hours to get to a hotel (the Sofitel opens at T5 soon, the Holiday Inn and Jurys are a 5 minute cab ride from T5), consider the Yotel in T4. You get a room for a minimum of 4 hours, enough to lie down and get a brief nap in a clean, private, cabin.
I would never consider sleeping landside in a terminal, sorry...
S.