You should let your hair down.
【讲解】to let one's hair down 的引申意思是指轻松、自然，或把心理的话说出来。
The president has to make so many official appearances that he seldom gets a chance to let his hair down and enjoy life like ordinary people.
Sally, we've been good friends for a long time. But lately I get the idea you are very much upset with me. I wish you'd let your hair down and tell me what's wrong to make you feel this way.