Sleep Tight «Firefox»

Light is the enemy of melatonin. "Sleep tight" requires absolute darkness. Not "dim," not "twilight." Dark.

Interestingly, the famous second line—“Don’t let the bed bugs bite”—is a much later addition. It doesn’t appear in print until the late 19th or early 20th century, well after “sleep tight” was already established. This suggests that people heard the alliterative “sleep tight” and wanted to add a playful, slightly scary, and memorable couplet. The bed bug line is a joke, a gentle tease, not an origin point. Sleep Tight

Title: Sleep Tight (Spanish: Mientras duermes) Director: Jaume Balagueró Genre: Psychological Horror / Thriller Country: Spain Light is the enemy of melatonin

Origins likely refer to:

Full rhyme:
Good night, sleep tight,
Don’t let the bedbugs bite. Full rhyme: Good night, sleep tight, Don’t let

Caffeine has a half-life of 5 to 6 hours. The quarter-life (the amount remaining when you try to sleep) is 10 to 12 hours.

While the film uses the phrase ironically, the idiom itself has a rich history.