First of all, thank you for coming to this forum for help as the group of people on this forum have a wealth of information (more than 90% of the Dr's I have seen) and are always quick to provide any assistance they can.
I have had CRPS for 4 years and I have never experienced the random passing out that you have described. With that said, I agree that it could be a medication issue. While it is possible that he is taking too much of his medicine, it is also possible that his medication is causing his blood pressure to drop to low levels which may explain the random passing out. CRPS does mess with a persons blood pressure and I monitor my on a regular basis (as mine reaches incredibly high levels) but I have heard of the opposite happening. Also, I have heard one medication that causes simular passing out issues and that medicine is in the neurontin family. I would definitly address your concerns with your brother ASAP as each fall can potentially cause additional issues with his CRPS. Eitherway it does sound serious. Thank you again for visiting the forum and please don't hesitate to ask any questions that you may have as this disease is not easy to understand since it is rare and has only had what I consider minimal amounts of scientific research.
Sarah