Waking up screaming?

My LO is a little over 4 mo, recently (last night and the one before) when he naps or asleep at night, he will be sleeping and then all the sudden start scream crying. He used to stir, roll around, start to cry and then his cry would increase if not attended to quick enough. Now, my LO will be sleeping and then immediately start screaming. I haven’t switched anything food wise or formula wise (he gets both). I’ve tried gas drops w/o success. Peeing and poo normally. I guess this is just part of the sleep regression but it seems different. Any ideas?