Why do my neck muscles spasm when i start to yawn? it happens more on the right side and the vein/tendon spasms for a sec and i have to stop yawning.

Normal variant: Likely this is not a medical disease or definable condition unless other muscles affected or you remain in that position for a while. Some medications like anti psychotics and antidepressants can do this or electrolyte imbalances also but usually a passing symptom. If continues or affects other muscles, see a neurologist.

Cramp: This is merely a muscle cramp similar to muscle cramps in your leg or foot brought on by certain movements. They don't have the same significance as spontaneous muscle spasms occurring in scattered areas of the body related to deficiencies of magnesium,calcium or potassium.

Visit a neurologist: You have cervical spasm; ; 1. dehydration, with electrolyte imbalance -treatment -hydration and electroloytes. 2. Nerve injury or pressure to a specific cervical nerve roots. That will give spasm and possibly segmental numbness, weakness and pain. 3. cervical dystonia.-Rare; forcible contraction of neck muscles with with stimuli like yawning or stretching. can be familiar; 4. MS, ALS, Devic'