I can’t stop thinking about what could’ve happened and it’s driving me insane

Two weeks ago we went over to a friend’s house for their daughter’s 10th bday party. They have three girls, youngest two share a room and are 4 & 5. We took our two year old son and he was playing in the girls room with their toys when my friend had to run to the store and asked me to go with her. I popped my head into the room before I left and son was quietly playing with the girls toys, so I told my husband he was in there and we left. When I got back my husband said he walked in the room to check on our son and he has climbed up to the top bunk and was leaning off the side and spinning the ceiling fan… I said well he would’ve landed on the lower bed right? (It’s T shaped) and he said no it was off the far edge and he would’ve dropped 8ft onto the wood.

I cannot stop imagining him leaning too far and tumbling off and landing on his head. I keep imagining walking into the room and he’s laying on the floor motionless. I keep thinking what would happen if I lost him and he died. Then I think of all the ways I would off myself if that’s what happened. I can’t stop replaying it over and over and have even started thinking about having a second baby bc if anything happens to him, I will have to off myself bc I would have no reason to live anymore.

Someone please help me.