sorry for taking so long to get back to you Leslie, for a while I had lots of trouble typing in my user name and getting all the threads I posted in to show up, so I lost track of this one...but it seems to work now.

Meds like amitryptiline, lyrica and gabapentin can affect the sphincters and how they work in the body. Anticonvulsants and antidepressants and for some the benzodiazepines can affect the spasms occurring in the body's sphincters, and muscles (relaxing/calming/quenching burning and spasms/cramps).

So, when the levels of these drugs increase or decrease ( either through adding another medication that can interact with these) then you can get less or more spasms/cramps/burning.
so if your oesophageal sphincter started to spasm and oesophagus spasms and bowel spasms it would explain you throwing up.
The helicobacter drugs could've interacted to cover you better or/and seeing you're switching to Lyrica... you could be not on the equivalent dose of neurontin you were on yet and your body is withdrawing from the neurontin.

People with neuropathic pain who have been on these meds for long periods become centrally sensitized if they weren't already to begin with due to their injury and it can spread to other parts of their body. Internally, the gut contains nerve receptors that don't respond the same way ...everything slows down (slows down cramping/spasms/) and GI tract slows.

I don't know how the thyroid meds would affect this process...perhaps lookin up their side effects will give you an idea.

I'd Keep away from all stimulants coffee, sugar etc and try to keep your body on the alkaline side as much as possible....no laxatives either...this can start off the vomiting during the bm. THere is also a connection between the enteric nervous system (ENS) and the central nervous system (CNS), I understand it occurs through the vagal nerve. THis can explain vasovagal syncope (complete blackouts) or to a lesser extent, dizziness and starting to throw up, whilst having a bowel motion.
This is very scary, I know. Hope some of this helps. Take care.