Is it the ceiling thats warping? And if it is the ceiling, does it feel firm, or does it have give?

If it’s not the ceiling and is just the trim I’d just pop off the trim and reposition it. If it’s the ceiling and it has give id probably do the same thing. If it doesn’t have any give and is actually the ceiling settling oddly I’d say you probably should have someone come and take a look at you foundation, especially if you notice a lot of cracks near windows/doorways.

If it’s the ceiling and you want to do the good ole landlord special, I’d just fill it with some joint compound, texture and then repaint it.