My T said it can happen with PTSD. I have PTSD and will get sick sometimes when I am under too much emotional stress. T said it is a part of the flight or fight response. I also heard it had something to do with man's evolution. If a predator saw the prey vomiting, the predator would be more likely to not kill that particular one as it may be sick and eating it would not be wise.

I also found this link for you:

http://www.wellsphere.com:83/brain-h...nd-ptsd/775880