In the back of the SK lounge in T3 there are sofas where one can lie down - sometimes they turn off the lights from 2ish to 5ish in that area, sometimes they don't.
There is food available (limited in the middle of the night) and drinks.
The free cinema has really plush, comfortable seating (T3) and rotates thru a set of movies every 2 hours or so - may ormay not be to your taste but they are listed and it's free - pretty much at the opposite end from the SK lounge. It is often VERY AC so bring a jacket or...