I'm curious how emetophobia became a problem for people

For me personally when I think back to my childhood I used to be HYSTERICAL if someone in my house was poorly and I was a very anxious child but emetophobia was definitely not a daily problem. I can't think of anything in my childhood that could have caused my phobia. Although, I did have an accident when I was 3 where I knocked my front teeth out and I can't remember it but my mum is certain this is the cause becaus she said my mouth was full of blood and she thinks my 3 year old brain made some kind of association.

Then on my first day of year 10 (I was 14) there was a boy in my class who was GREEN. I remember watching him like a hawk and I remember I couldn't think about anything except watching him incase he v*. Then he did. I saw it coming so I looked away and covered my ears. The whole class was pointing and laughing so I tried to do the same. But my face was burning and my fingers were white from pressing on my ears and my heart was going crazy. Then he left the class and went home or whatever. The lesson continued and it was like something just snapped in my head. All of a sudden all I could think about was v*. When I was certain the boy had been sent home I went to the school nurse and told her I felt n* and got sent home. Then I didn't go back to school for about a year. It was all I could think about.

I'm now 23 and i've lived with severe emetophobia ever since.

Is my story a common/unusual cause for emetophobia?

What triggered you?