OK, The farthest back i can remember is when i was in year 1... (not sure if i had this phobia before then but pretty sure this is the earliest experience)
It wasn't me, it was my best friend in year 1, and not sure if you have them where you are but there are these ice creams that used to be called "jokers" and they were like bubblegum icecream, blue, pink and green - anyhoo... we were doing some project at our desks in groups and there were egg cartons and seeds in them and my best friend at the time v* all over the table after lunchtime and it was the colour of this icecream (which i never ate from that day onwards) and she was hysterically crying and shaking the whole time, and i was the one who HAD to walk her to the front office where they were going to call her parents etc ... - I don't actually remember feeling any fear when she was sick at the time, i think watching the way she reacted with that situation it must have triggered a receptor in my brain to think "This is how you handle the situation".
So i THINK that is why i have the fear and i freak out at the thought of being sick because that's the way i thought you reacted?? if you know what i mean.
I don't know, that's my take anyways, and my old pshycologist i went to years ago said that to me also, but that truely honestly is the earliest story i remember so i'm pretty sure that bitch gave me the phobia!!! hahaha