In my experience nightmares are invariably caused by discomfort or pain while sleeping. This seems to apply to most individuals.

I tend to wake up screaming or in panic at the first sign of pain so am able to avoid the nightmares usually but I have RSD dreams when other symptoms appear. These are hard to describe but it usually involves shallow sleep and a sense of dread.

I'm pretty lucky with sleep most nights since the medication suppresses symptoms long enough to drift off and the pain tends to stay away while I'm asleep. It shuts off like one of the senses at night. This was my big problem with lyrica; every time I'd start to drift off the pain would get worse.