i think if it's an unusual thing, it can be downright painful to get your "normal" back. DD spends one day a week with Granma, and after several weeks of thinking "why am i doing this" she's actually fallen into a routine with that day too, and her sleep isn't impacted by it any more. to be honest, it's more difficult to get her to sleep at the end of the week if she DOESN'T have that day out! she knows mummy works a few days, then she has a day with granma, then mummy is home - if she doesn't get the day with granma between mummy working and mummy being home, she is all messed up

she also had her first sleep over last month and we had zip problems afterwards (which shocked me BIG TIME!)