(deyim) Worry about someone or something a lot, sometimes when one should be sleeping. (Often used with any and the negative.)
1. Yes, Kelly is in a little bit of trouble, but I'm not going to lose any sleep over her.
2. Don't lose any sleep over the matter. I refuse to lose sleep about it.
If someone, especially a child, sleeps over in a place such as a friend's home, they stay there for one night. She said his friends could sleep over in the big room downstairs
{i} staying as a guest overnight at someone's house; instance in which friends stay overnight at the same house (often in the case of a children's party)
A sleepover is an occasion when someone, especially a child, sleeps for one night in a place such as a friend's home. a party for children in which they stay the night at someone's house