I don't really know where it started to be honest.
When I was a kid I definitely suffered from anxiety but it was relatively infrequent and always passed off as being a "bug". I would wake up during the night thinking I was going to be sick, but as a young child that's all I could interpret it as.
When I was 11, they took me into hospital for testing because I couldn't eat. I had everything tested and probed and I left the doctors scratching their heads. It was on and off for 5 more years while I circulated doctors offices being misdiagnosed, scared out my wits, having panic attacks and feeling very ill every day. Finally I saw one doctor who saved me sooo much by recognising the problem and sending me to a psychologist after routine testing.
I have the NHS to thank for why it's this bad today, in a way, haha