baby having nightmares ?!

♡ 𝓚𝓪𝓽𝓻𝓲𝓷𝓪 𝓵𝓸𝓾𝓲𝓼𝓮 ♡
My 4 month old son can sometimes cry with his eyes closed and it's a different cry to any others I've heard. He sounds distressed like he's in a panic and very rarely does his breathing pick up speed from it but as soon as he hears my Voice he stops crying and sleeps again but if he's too worked up I've got to humm to him while stroking his forehead for him to quieten down and sleep again
Is my son having nightmares ? Like, is that a thing ? With him being young I wasn't sure