Night waking

Hi, hoping you all have some advice or insight as to what's going on. My 18mo usually wakes up and rolls around, sits up, etc a few times a night and goes right back to sleep on his own no problem. But for the last couple months he's been waking up once some time in the night and totally losing it - crying, screaming, throwing lovey out of crib, inconsolable. The only thing that gets him to calm down and go back to sleep is a bottle (the only bottle he still gets, and only bc I'm desperate and exhausted). The timing of all this varies - sometimes it's a couple hours after he goes to bed, sometimes not until 1am or even as late as 4am. I haven't found a consistent pattern. I try to make sure he eats a big dinner but he's also a very picky eater. So I don't know if this is happening because he's truly hungry or what the heck is going on. I'm not comfortable just letting him scream himself back to sleep, which is what my SO wants me to do. And I'm pregnant and due in 3 weeks so it'd be lovely to figure this all out before I have a newborn to deal with as well 😬

Any idea why this is happening and how best to stop it?