How to get over fear of sids? I can’t sleep or leave my son

My sister and I were pregnant together. We’ve always been best friends so it was amazing. We had our little boys 3 weeks apart. I absolutely adored my nephew and he was like a light in my life. I love him so so much and had so many plans for us and our sons. My nephew passed 7 days ago. He was 2 days away from 6 months. It was traumatizing, it hurts and I’m so mad. They were a couple houses away at the time and my mother ran to my house As soon as my sister found him. I can’t forget the screaming. I held him one last time yesterday and said goodbye. It’s so hard. The autopsy showed that there was something wrong with his brain stem. They’re doing more tests to see what exactly. But now I’m terrified. I can’t sleep. I have dreams and daydreams of waking up to my son dead. He just learnt to sit and falls back into his head. Sometimes I’m not quick enough and he hits his head. I’m terrified each time he’ll get brain damage. I’m so so scared my son will die too. And I don’t want to tell my family at all because I feel the last thing I should be worrying about is anyone but my sister and nephew right now. How do I get over this fear? My heart is hurting so much and now my head is filled with fear. The deepest fear I’ve ever experienced. Mourning my sweet nephew and trying to keep it all together for everyone is hard. I never thought this could happen. I need to get over this fear so I can sleep and be a better mom and just feel a like bit of peace. How can I get over this? I can’t do counseling because we are locked down and I can’t talk on the phone because I’ve always had bad anxiety with that. Should I reach out to my doctor? Or is this something I can slowly handle myself? Does anyone have any advice please?