تعریف و معنای "[let] {one's} hair down"

What is the origin of the idiom "let one's hair down" and when to use it?

The exact origin of the idiom "let one's hair down" is not well-documented, but it is believed to have emerged in the 19th century. It likely draws from the practical act of women literally letting their hair down from more formal, restrained hairstyles when they wanted to relax, as mentioned earlier. Over time, the phrase became a common expression in English to describe the act of loosening up, being more casual, and embracing a carefree attitude.