Immediate pain relief can be achieved through multiple options from ultrasound, IFT (even though you don't appreciate it), trigger release, dry needling or any other possible modality or manipulation technique that may be required. Which modality or technique will be beneficial can be determined only by physical examination by the Physiotherapist. However you will find a sustainable solution only if you religiously work towards strengthening your upper back and neck muscles. Postural correction and ergonomic rectification at your work place will be essential.
Next Steps
Please try and visit an orthopedic and undergo radiological screening to ensure there is no other underlying pathology to your muscle spasm. Follow up with a Physiotherapist to ensure that you get relief from your acute pain after which an appropriate rehab plan is defined for you. And more importantly you follow it! Long term maintaince can also be achieved through yoga, which will ensure appropriate muscle stretching and strengthening. Of course you need to practice yoga with someone who is good at it.
Health Tips
I am assuming you would have already tried home remedies. Don't overdo it. Get a qualified opinion at the earliest. Wishing a speedy recovery.