Do people flinch normally ?

I've always had that thought, why do i often flinch everytime someone raise their hand near me? Why do i cover my head or face so the impact of any potential hit wouldn't hurt that much, Is it because my of my friends who hit eachother jokingly? Or something completely different? I love my dad and he loves me too but he has really bad anger issues, he try to control them, also take medication, but when me and my siblings were younger, he used to sometimes hit us for god knows what and the shouting and the loud noises of things throws around in anger left me terrified till today, maybe that's why i hide in the bathroom whenever there's a fight or yelling around the house, maybe that's my hands shake, my eyes gets glassy and my breathing gets heavy even today, OR was it because of that past religious school where for one mistake you get hit so hard in your back or should, it leaves you aching for a few days or maybe faint bruises that i always ignored.