Overprotective, anxious mum

My son (5) jumped into a pool at a friend’s son birthday party and was struggling to stay afloat even with his jacket on, I shouted for help, I jumped in to get him and nearly drowned since I cannot swim due to a traumatic event when younger. My partner than had to jump in after pulling my son out the pool to get me, turns out this pool was 8ft deep which we wasn’t told. I cannot stop having flash backs and nightmares of that day.

I went to get a cow and calf in yesterday since we farm, made my son go the other side of the electric fence as I won’t trust the cows in that state of mind, I told him to walk along the fence, over the fence which is by my partners caravan and wait by the closed gate for me as would walk past it to get to the farm, I was fine until I remembered there was a river that ran next to the gate, about 5m away from it. I panicked and kept imaging him in it and struggling and that every second went, I would lose him, I left the cow and calf and was screaming his name and running towards the gate… of corse he was stood on the gate picking a leaf apart, wondering what I was screaming about…
I have dreamed of him drowning for nearly 3 years now,
I struggle to let him do some things as I always imagine the worst.
Does this feeling ease as they get older ??