True its no way to live. I have a small amount of paranoia which I talk myself out of. I have to buzz people through twice and unlock my flat door. Good thing I can see and hear who I’m buzzing in.
Most of the time I’m expecting someone.
It does make me jump but not in the way you describe.
I don’t know what to suggest apart from reading loads about PTSD and practicing what coping skills the reading material suggest.
Practically wise maybe you could send deliveries to an Amazon pickup point or an Amazon locker.
A lot of supermarkets do click and collect these days.
Not much help though if it’s the TV licence people or the gas man.
Sometimes I don’t answer if I’m not expecting anyone.