My doctor and I were having a chat about this one time and he said that yes bags are caused by too little/too much sleep, fluid retention etc. But he said that another reason is weight loss or gain. At first I was like what, are you trying to tell me I have fat eyes lol but he said that if you lose a significant amount of weight off your face then you have slightly excess skin around your eyes where there used to be flesh, and that excess skin then just droops into bags. Now my bags aren't that bad, I mean I don't have huge folds of skin or anything but I have permanently discolouration and a few very fine lines, but because they are there regardless of how tired/fresh I am, I've put them down to slight weight loss, about a year ago. (I lost weight off my face first). And there's nothing much you can do about that! Good make up, teabags/spoons etc will make your eyes look brighter short-term though.