4.5 months old crying in sleep

Hi mummies, my 4.5 months old is waking up and crying inconsolably in his sleep. His eyes are closed, so likely to still be asleep but is screaming and crying. It happens 3-4 hours after he falls asleep at night. Any one has similar experience? It’s not hunger/ teething.... and I think he just passed his 4-mth sleep regression too 😣