help please

my son has had night terrors sice the day he was born. (thank you mother)little back story: I had night terrors when I was younger but now I hardly have even dreams, my little sister had them, my grandmother had them, but my mom on the other hand still has them and she too had them since the day she was born. now my son is 8 months old a few month back when he was four months his Dr prescribed him some allergy medicine because his allergies we're bad like runny nose every day sneezing all the time bad so I give him .25 teaspoon every night before bed (it helps him sleep) since we started he's only had maybe two night terrors a month from the previous almost every week. which I am so thankful for because I hate hearing him cry bloody murder. but now m husband and I have ran into a problem. we used to have to splash cold water on his face to wake him up but now as of last night even that didn't wake him we thought it did but then I noticed his eyes were still glazed over and he was still sleeping even though his eyes were open. I hate this. I hate seeing my son cry and I can't fix it. I hate knowing something scares him and I can't fix it. I don't know what to do anymore. I plan on talking to his Dr at his next appointment about it. do any of your little ones have this problem or even you? how do you wake them up? when I have nightmares I can usually wake myself up but obviously that's hard for such a tiny baby. he is so precious and I hate knowing that something scares him so much.