Suggest Remedy For Frequent Nightmares In A Baby

My 9month old is waking up 2hours after going down for bedtime. He imstarts off crying and then sits up and screams and then stands up in his crib and crys some more. I go in and comfort him but sometimes he refuses me also he seems very freaked out that im there. Some nights are easier then others. He goes back down after 5-30minutes after the episode. Im wondering if he ia experiencing a nightmare or a night terror? & what can i do to help the situation. He has had a bedtime between 7/730 since he was 3 weeks old and gets up at 6AM and goes back dowb for a 9AM nap and so on.. What can i do to prevent these scary moments for him?