Sometimes, i wake up with one of my upper trapezius muscles completely contracted. then it spasms for several days. how can i treat/prevent this?

See your doctor: The underlying cause of this may range from a simply muscle sprain to a cervical herniated disc. You will need to be evaluated, and if this continues despite nsaids, physical therapy may be helpful. When these fail to relieve your symptoms, or if you have progressive weakness, arm/hands numbness tingling worsening, then further work-up with e.g. Cervical spine MRI may even be indicated.