I haven't barfed in a therapist's office before but I often get super nauseous while anxious. That said I tend not to eat anything before sessions, so hopefully if it ever happens I wont have much of anything to vomit.
I probably would have barfed before having an invasive kind of ultrasound, genital. Like, I was eyeing the trashcan and feeling like I should get over to it, when I was called into the back. Then I kinda went into dissociation mode. Lucked out on that one.
Today I have an appointment (therapist) and I have been nauseous all day.
Also I do know someone else with PTSD, who has barfed in her therapist's office.
It might feel embarrassing but I am sure you're not the first person to have that happen with your therapist, I'm sure they know that it's a possibility, are trained for it, and would be empathetic to what's happening to you.
It's not like we can control our bodies :/ sadly, lol. So, it's something out of your control. Just like any other trauma reaction, anything anxiety, dissociation, etc. can physically cause. I don't have control over my legs violently shaking at appointments, with my shoes doing a very fast staccato TAP-TAP-TAP-TAP-TAP-TAP-TAP-TAP-TAP-TAP on the floor, despite the fact its embarrassing to me - even if I try to physically force my leg to stop moving, using my hands, I can't.
I hate coming out of an appointment drenched in sweat like I just did a rigorous workout - I feel super embarrassed coming out with my hair all jacked up (once it gets a little wet, it goes crazy), wet from sweat, I just look like a mess.
But, I have no control over those things. Same thing applies to barfing in therapy. It sucks, it's horrible, it makes you feel embarrassed, but you can't control what your body does of its own accord - and your therapist knows this. If your body really wants to barf, its gonna barf. If it wants to shake and sweat, its gonna shake and sweat. They're all just involuntary physical reactions to stress/anxiety/etc.
It helps me to think about that. I dont like my body's reactions - they are uncomfortable, they make me feel embarrassed, and I can't control them - but the therapist's office is a safe, private space to have those reactions without judgement.