The Cervical MRI being negative does not mean you don't have an upper neck injury. The muscle spasming is enough to support a diagnosis of subtle cervical injury. I suggest you focus on your neck and back. Finding a way to sleep in a straight posture will help. When my neck was at its worst, I slept in a recliner. This prevented me from rolling on my side and causing neck trouble.

Getting relief from pain will help your brain relax. Then, it can try to heal.

My best to you.