An MRI can only see items the size of a BB or a bit smaller, maybe down to a millimeter if the MRI is high power. They can not see the microscopic damage to cells.

Brain stem injuries are often not a severe damage but rather a dysfunction that arises from inflammation in the area. If a brain stem injury was more than that, you would be permanently disabled by it.

The inflammation that can arise from cervical vertebra and the associated connective tissue can come and go with posture and other factors. be very careful with chiropractors. Some are overly aggressive with the neck and like to twist and pop more violently that an injured neck may tolerate. That is why some of us have turned to Upper Cervical Chiropractors and their much more gentle and focused techniques.

I doubt your gabapentin dose has any effect on your memory. Your breathing will have a very big impact on your memory. Your brain needs to sleep with a good supply of oxygen to properly reformat the events of the previous day. Without this good oxygenated brain functioning, you brain acts like a desk covered with scrap paper notes all mixed up.

The key function of your brain during sleep is to clean up the previous days desk top of scrap paper with memories written on it and file them away in an organized fashion so there is room on the desk for a next day's worth of memories.

Anxiety makes that heap of scrap paper even more chaotic to sort out. The brain wants to get things sorted out or it will just continue to overload.