17 month old screaming at night?

My 17 month old has never been a great sleeper, but lately he will wake up in the middle of the night just screaming and crying bloody murder

He does it every few days, and i can never find anything wrong (except scratching his skin which he does often cuz of eczema) and he calms down when he sits with a toy after a while…

He eventually falls back asleep but it confuses me so much.