Bit of a weird one this; but I've experienced both, either constantly eating, snacks and everything, even after a huge meal and still feeling hungry, then on other occasions totally off my food for days, both episodes were due to dehydration.
The always eating, was my body craving fluids, which my brain mistook for hunger rather than thirst.
Although, when off my food, I was normally admitted into hospital via Ambulance for IV fluids and within maybe 20 mins of receiving fluids, my appetite had returned.
This was before takedown surgery and whilst I had the loop ileostomy.
The dehydration use to creep up on me, the lack of potassium in the brain as a result of the dehydration also affects brain function.