Doc thinks very tight scm muscle is the cause of dizziness.stretching daily, 2x week massage therapy for 2 weeks, still bad. how long to get relief?

Depends: It depends on the specific cause. Having a tight SCM does not directly cause dizziness, but there are conditions that can cause a tight SCM and dizziness. It is somewhat a generalization, but most dizziness is either middle ear or intracranial related or from a system is cause such as low blood pressure, medication reaction, cardiac source etc. So, primary diagnosis must first be pursued.