My ds (3.5 months) has started doing this in his sleep recently. He's sleeping next to me in a crib and it can go on for about half an hour, quite violently. I gently stroke his face or gently rub his chest and eventually he calms down and he is asleep throughout. Is there any reason why he does this? Is it a nightmare or just perfectly normal? His mattress is covered in hair every morning so is definitely going to end up with a bald patch. That is the last thing I'm worried about but am just keen to know nothing is traumatising him in his sleep.