Hello I also had a nissen and I have seen specialists in the UK the US and other countries with the problem of dry heaving or retching where nothing comes up. I also collapsed and this turned out to be that my Vagus nerve was either damaged or cut during my Nissen and because the food went through my stomach to fast causing me to collapse. Finally a consultant here in London sent me for a test which involves eating radioactive potatoes which showed that the food was passing through my stomach in 11 minutes which is half the time it should take.
Because the food is not digested properly the large intestines called for more fluid to help to digest which caused the collapse. He prescribed Amitrptyline which one of the side effcts is to slow the progress of the food through the stomach. I retook the potato test and with taking the medication the food took 22 minutes to pass through and the the retching stopped. It is extremely important that the surgeon takes care not to damage the Vagus nerve. It took 5 years to find out about tyhe Vagus nerve problem to be diagnosed. I had 9 endcoscopys visiting the states Panama Venezuela before i found the problem. If you want to email me about this my email is
<Edit> I have removed your email from your post . It is recommended to not post your email address in the public forums. This is easily harvested by spammers and others. You can display it in your profile to be viewable by other members, if you wish, but they still may be potentially used by spammers. Email addresses in profiles are hidden by default.