Burning 800 cals overnight is expected and normal.
You burn calories sleeping. Your body still needs to breath, produce hormones, digest, and you do all that tossing and turning.
At your current weight of 363lbs, depending on age and height, your BMR can be 2400. That means if you slept for 8 hours (1/3rd of a day), you would burn 800.
Deb, in New Zealand