why do we lose weight over night?

[n9wiff]

You can sweat in extremely little amounts. You also lose a sizeable amount of water from breathing.

Imagine a glass fogging up as you breathe passively over it. That's all the water that will be lost and you will repeat that again and again.

Same thing with sweat, you body can just be kinda very barely moist.

You shouldn't lose much fat when you sleep because your organs and systems tone down significantly to save energy. Your expenditure would be very little.