My little bro gets really bad Nightmares?

Hi my little brother is 13 years old and he frequently wakes me up at night screaming across the hall waking up from his dreams. He always says "I can do this i can do this wait wait I can do this", or "no holly holly help help" (my name is holly). He always says stuff like this. Me and my cousins talk in our sleep but not yelling and only sometimes (hereditary?) anyway is there something wrong? I feel bad because it keeps interrupting his REM sleep and so he's always tired for school the next morning. He's too embared to talk to anyone else. Is there anything I an do to help him? Is this a really bad problem?