something healthy

One late night can lead to another and another When you have one late night you can usually function 'ok'. The following day is when it can catch up to you.
If that is followed by another late night even if you get 7 hours sleep you will feel terrible. If that in turn is followed by another late night again with 7-8 hours sleep you will continue to feel terrible. And the cycle continues.

You have been on a diet for a period of time and gradually you have stopped losing weight. This happens too many and now is the time you take a look at your journal. Hopefully you have kept a journal and now you can compare what you were eating and doing when you were losing weight to now.
Look for changes in foods and amounts these are usually what happens. As you get a little bored or tired of the diet you change the foods to break the boredom.