Night Terrors

My boyfriend's little cousin, Jake, is 9 and he for the last year or so has been experiencing night terrors. I've actually seen him after he has woken up and he was afraid, but he had no idea why. Whenever he has these night terrors he can almost never be woken up and his night terrors have also caused him to wet the bed from being so afraid and unable to wake up to use the bathroom. He has even been tested with it and has been told that if his night terrors get much worse he could even scare himself to the point of where he could die. Now after learning about it i can understand why it is so hard to wake him up. I never thought so in depth on it before today, and now i'm going to worry about him more.