Sleeping in T5
I recall watching "Airport" on the BBC some years ago and watching the police moving people on who were trying to sleep landside. Airside may well be different; the first time I went to Australia (mid 80s) our plane was about 5 hours late and left at 0230 and nobody tried to stop us going anywhere in T4.
I did once (79) arrive in Delhi at about 2200 (from Calcutta) with a connecting 0630 to Jaipur next day and ended up finding a quiet corner to try and get a little sleep. It's not an experience I would want to repeat in any airport.