In Shakespeare's time, mattresses were secured on bed frames by ropes...when you pulled on the ropes the mattress tightened, making the bed firmer to sleep on. That's where the phrase, "good night, sleep tight" came from.
Video game trivia:
Pit, the main protagonist of the Kid Icarus games, was intended to appear in the original Super Smash Bros. on Nintendo 64. The developers were unsure about how to animate Pit's wings, so they scrapped the idea, and the Pokemon Jigglypuff took Pit's place in the roster. Pit eventually did make an appearance as a trophy in Super Smash Bros. Melee, and finally as a playable character in Super Smash Bros. Brawl.