You are over thinking it - but you are his mum & that's part of the job description
It is, however, time to let it go.
He is 4.5 months old, they change all the time. He isn't 'back where he was 2 months ago' he's like he is 'now'. Next week he'll be different again. They're funny little creatures who take a lot of their cues from their Mum's - so if anything, it's your anxiety he's picking up on. They're funny little creatures :)
It was a very small bump and he was in a very protective car seat. Babies regularly fall off of beds, down a stair or two, out of their highchairs/buggies/bouncers, even over a shoulder! If everyone who had a tiny bump like your DS did, didn't do contact sport then there wouldn't be anyone playing anything!!
It was an accident you didn't 'do this to him' - it's not as if you threw him on the floor or shook him.
Your DS is & will be fine but if you want to get him checked out by anyone else, I would take him to a cranial osteopath who specialises in babies.
I am far more worried about you. Your reaction is out of proportion to what has actually happened and you aren't letting yourself be reassured by professionals. I think you should go and see your GP and see if you have post natal depression. It's hormonal and nothing to be worried, embarrassed, scared about - but the sooner you get treatment for it the better and that's better for you and your DS.
Try to relax today and enjoy your lovely wee boy
