I imagine he's scared (and understandably so) and needs reassurance--to feel safe. I'd let him sleep on the floor in your room if he wants to. Or at least tell him that if he wakes in the night and needs to be near you, he can come in and sleep on the floor in your room. I did this with my son and he did not experience something so frightening. I think that once he feels secure and knows all is well and knows he can go to you whenever he isn't feeling so secure, he'll be fine.
He is still anxious about the storms reassure him that you are with him and that you will make sure he is okay, it is good you stopped the Meds if he didnt need them , most of them have side effects ,Time will help, but if you are living in an area of storms you have to accept most children will be anxious and upset, the only other thing to do is Move to another state.