Is it possible to arrive at night and sleep for a couple of hours inside the Brussels Charleroi Airport before taking an early flight? If so, are there any decent places to sleep/rest?
According to this Sleeping in Airports article, the airport is open 24h, but you'll probably have to sleep on the floor:
The airport is open 24 hours, but overnight campers will have to stay landside until security checkpoints open around 4:00AM. Seating is very limited and most have armrests, so bring along a blanket or sleep mat to rest a little easier on the cold floor. The far end of Terminal 1 has large windows and some private nooks. Do expect security guards to wake you up to check IDs or as the airport gets busy. For uninterrupted sleep, nearby hotels offer shuttle service.