乐不忘形lè bù wàng xíng

feel very glad but not to the extent of forgetting oneself
❍ 罗超乐而却不忘形，甚至更加注意自己的一言一行，力求处处得体。(王汶石《风雪之夜》52) He felt very glad,though he never let his feeling of exhilaration show too obviously. He paid even more attention to every word he uttered and every move he made,trying as much as possible to make them appropriate.