Another emetophobic here! I used to be so scared of being sick that I practically stopped eating when I was at sixth form college. People thought I was anorexic but it had nothing to do with my body image or anything like that, I was simply terrified of food in case it would make me sick.
I've been much, much better recently thank god. I think it's definitely closely related to other anxiety and stress in your life as when things are calmer and I feel more in control of stuff in my life generally, the phobia is less severe. It flared up badly during the year leading up to the break up with my ex and I didn't make the connection between the stress and feeling out of control, and the strength of the phobia until aftwerwards.
I completely empathise with the poster who said they are scared about being sick when someone else is around - emetophobia almost certainly has its roots in social anxiety disorder and the more I understand this about my own condition, the better I get.
I also have to say (and I know this will freak some of you out, so I apologise but I think it's important): one of the other things that helped me was catching a stomach bug. My partner at the time caught it too and we were both up all in night dealing with it together. In a very odd way it was kind of bonding - we ended up joking about who could make it to the bathroom quicker. Also, I remember thinking at the time, as I was vomiting, that 'This really isn't so bad. Sure it's unpleasant but not half as dreadful as it is in my worst nightmares'. I felt like such a hero afterwards because I'd lived through my worst fear and survived. It was almost like I was on a kind of high, and I've really tried to hold onto that feeling of flexing my muscles in the mirror and shouting 'bring it on!'. Lol.
Not that the answer is to go and actively catch a stomach bug. I know how terribly, terribly debilitating a phobia like this can be, but I just want to say that it doesn't have to be debilitating forever, it's possible to manage (if not completely overcome altogether - I still have wobbly days), and remember that you are in control of it, IT isn't in control of you.