I know exactly when mine started, I was 14 (so older than most here) and until then I had had plenty of sv and always been able to v without any major issue. This one time my brother had the sv, then the rest of my family and I was the last woman standing. I started feeling nauseated and I knew it would happen eventually, but could not force it, so I sat on the cold toilet floor for hours, waiting for the inevitable. I remember just sitting there, not knowing when this awful thing would start and while I was quite calm then and there (much more calm than I am now was I in that situation) that wait killed me. That sv also triggered coeliac disease, so I never fully recovered from that bug, feeling sick for years afterwards (though never v again for many many years). I used to take metoclopramide in secret before going to bed so I would be able to fall asleep nausea free.
Once I got diagnosed, changed my diet and stopped feeling nausea the phobia got better and I was able to live fear free for years, though hearing or seeing someone else ving made me a bit panicky, now I cannot even face it. I even moved to Africa for a year, ate most everything and was ok (though I had some antiemetics on hand, I never once v there! I did on a visit back home though).
It got really bad again less than a year ago. Unlike many here, I did have a few episodes of v in the last few years (three in the last 5 or 6 years, 2 of them made me go to the hospital not because they were particularly bad, but because I always hope they can give me something that will stop it. They never do in this country (the UK, they did in Spain where I grew up)) and still was sort of semi-ok (I do panic and cry and make it worse that way, but I don't die, which is what I feel like I will), but then when I read about noro this November, I just got panicked and now, 9 months later, I still am. I take antimetics fairly regularly, and have asked for mental health help and am nearly done with a "self help" CBT-like short therapy run (they only gave me 4 sessions).