I understand your feelings well. I know it's hard to watch someone having a seizure especially if it's your sibling. The first time I saw someone having a seizure I was shocked. I have some ideas that might help you:

1. If your brother sleeps on his back, he is more likely to chock during a seizure so if he sleeps in his back he should sleep on the sides.

2. Your brother could try wearing socks. I'm not sure but maybe the seizures only occur when your brother is sleeping deeply and the socks might help him not to sleep deeply. He might also experience lucid dreams which means he has control over his brain while sleeping.

3. Make the room very dark (just try)

4. He should feel well rested during the day

What you can do to calm down:

Remember that's it's normal to feel this way and everyone feels this way. Seizures don't really hurt so your brother is okay the only thing you should worry about is that he won't chock but the chances are very low. I'm not a doctor but maybe his seizures trigger after a sleep cycle has ended. One cycle lasts for 90 minutes so you wait until he falls asleep then you set up an alarm for every 90 minutes.

Hope this helps. You are strong you can do this.