As ironic as it sounds, our population has forgotten how to breathe. Most discomforts in the middle and upper spine(and even in the neck) come from improper breathing. How's that? Stay with me.
There's a muscle in our body called diaphragm. It's also called the BREATHING muscle. It looks much like an umbrella and it splits our abdominal cavity into upper and lower part. When it's used to breathe, it allows the lungs to expand bellow our chest into the abdominal.
Now why would that be important?
When you're using your chest to breathe, you lift it up. Take a deep breath and see for yourself. Besides lifting your chest, you also make a curve in your upper spine as you breathe in. And THAT'S the problem.
Your spine is made out of 26 bones, 24 of which are separate. They're called vertebrae, and they can hold immense forces IF they're stockpiled correctly. The spine itself forms a double S, and while this double S is formed, the vertebrae are directly one above the other and there are only compression forces among them. And compression forces are NOT a problem for our spine.
The problem are SHEAR forces - they appear when 2 vertebraes aren't directly one above the other, meaning they are compressing the disc between them on one side and pushing it out on the other, while your spine goes out of it's natural curve.
And this happens when you use your chest to breathe. Your spine isn't aligned as is should be, and shear forces are all over.
That's why I encourage you all to start doing breathing exercises daily, until breathing through diaphragm is like second nature to you. One of the best(and essential) things we can do for ourselves in the long run.
Here's a clip of my last session. The point was not to lift my chest throughout the whole session, meaning, I've been trying to breathe through the diaphragm for the whole time.
Special thanks to 
Peace!