Last year I did a mileage run LAS-SFO-PHL-TPA-PHL-SFO-BOS-IAH-SJC (all in Y). Got on the plane at 15:05 on Wednesday and got off the plane 19:45 on Friday (almost 53 hours). There were obviously some connections which gave me 3 or 4 hours to relax but it was two overnight flights back to back and I didn't leave the airports.

I could never sleep on aircraft until I did that run ... now I can quite happily fall asleep within minutes of getting airborne ... I suppose it was worth it (though never again!).