What is sleep tight?

"Sleep tight" is a commonly used expression in English, often employed as a friendly way to wish someone a good night's sleep. The origins of this phrase are somewhat debated, but it is generally understood to mean sleeping well or deeply. One popular theory is that it dates back to the 18th and 19th centuries when beds were supported by ropes. To ensure a firm, comfortable sleeping surface, the ropes needed to be pulled tight. Thus, "sleep tight" would imply a snug, well-supported sleep.

Another interpretation is simply that "tight" may have been used colloquially to mean soundly or well, without a direct reference to bed construction.

The phrase is often paired with "don't let the bedbugs bite," creating the rhyme "sleep tight, don't let the bedbugs bite," which adds a lighthearted, humorous note to bedtime farewells. This complete expression is generally intended to convey warmth and concern for the other's comfort and wellbeing.