Trapezius muscle pain relief

I had this so bad one year for about 4 months I was almost in tears and became depressed. It all started when I was polishing stainless steel boat railings with sandpaper and steel wool using downward pressure with arms doing and up down motion for hours a day. The thing that broke the pain was physical therapy via hot towels, human deep massage and electrical muscle stimulation (via machine once or twice a week for 15 minutes) for about 6 weeks. However, by the end of the first session the excruciating pain was greatly reduced. On the second round a day later I left with virtually no pain. My symptom was I was walking with one shoulder down ( or one up ?) observed by friends.

Here are the common movement patterns or daily habits that can contribute to trapezius pain (when all combined):

1. Typing for long periods of time (2). Especially if the desk height makes you elevate your shoulder to reach the keyboard. Check my video tutorial here on how to sit properly to avoid muscular pain.
2. Shrugging one shoulder up to hold the phone between the shoulder and the ear.
3. Carrying a backpack or bag on one side.
4. Repetitive movements like playing the guitar can tighten the elevated arm side.
5. Sitting hunched over
6. Pulling the head forward to read small text on the desktop monitor for hours each day (this promoted forward head posture which triggers upper back pain).