This is a two part, because this could apply to both my conscious and unconscious self. I think the most horrific thing that haunts me is tornado, both when I'm awake and when I'm sleeping. I can't really say I've even been in a scenario that might give reason to such a fear. But it's there anyway, hiding under the surface. [Well I have seen tornados off in the distance, but never so close to warrant a reason for the panic attacks I get now.]
I suppose the thing about tornados for me is that they are a force of nature that can easily kill you. It can't be stopped. It can't be killed. All you can hope to do to survive it is run and hide in a place where it can't reach you, even then it has the power to ruin your life.