I wouldn't have any experience in dealing with the brain damage (if thats what it is) aspect of this. However, I do suffer from migraines and nausea brought on by anxiety. I also have trouble with not being able to focus/concentrate or even remember things both short term and long term. I'm guessing that because of the stress of the violent relationship, it brings on a great deal of anxiety in many ways. Migraines can be caused by anxiety.
I would talk to a doctor and see about some sort of migraine medicine like topamax for example. Or possibly even an anxiety/depression medicine.
Let us know what happens!