Where did all the weight go overnight?

[GlamGuru]

Ok so I ate dinner, and measured myself on a scale and it reads 62kg, ok so it's the food. After I sleep and wake up, it's 60.5kg, wtf? where did it all go?
And why am I so hardstuck at 60kg? I can never get higher despite eating to 62kg, it all just disappeared.
It's so fucking hard for me to gain weight.

 

[fishfish]

moisture loss from sweating + breathing

and also just burning fat while your sleep