I think you're on the scale too often, I don't play that game anymore. I weigh myself once a month or so. That little amount of weight that you lose in your sleep does not matter, changes over longer periods of time are a better way to gauge progress, but the mirror and by feel are better for me. I remember when I was just starting out and would weigh myself 5 times per day, I drank alot of water then just so I'd weigh more,lol.
i remember one summer morning when i slept close to 13 hrs i lost nearly 10 lbs of water weight, and this is on a 5'6"-7" frame
feels weird thinking you've gotten too fat or have gotten gyno the night before when you wake up realizing that its all water weight and you're actually pretty lean...
and yes you lose weight from urination, hydration, respiration, and maintaining body moisture (evaporation), and sweat. it all adds up if you sleep a lot in any given night