Question
Pain started in right upper back w/spasm; radiated into shoulder and right lower arm.  I have a throbbing ache constantly in right arm.

Answer
John,

Since you understand that you have a muscle spasm, the question becomes, "how do you end the spasm?"

Please see the article,
Pain Relief through Movement Education (sensory-motor integration) -- Explaining Hanna Somatic Education? at somatics.com/page4.htm.

I would suggest you see a clinical somatic educator.  list:   hannasomatics.com/practitioners

Alternately, you can use the self-help program, The Cat Stretch, found at somatics.com/page7.htm.  A modification of Lesson 1 will probably clear up your spasm.

with regard,
Lawrence Gold