Re: Back pain turns to numbness???
It sounds to me like it could be a pinched nerve, maybe in your cervical spine. Especially if you have numbness & pins & needles in your arm. Spine problems in the upper back/neck area can also cause shoulder pain. And all the pains dont necessarily always occur just in one spot, they can radiate all over the place. There might have been a disc herniation that first caused muscle spasms in your uppper back (spasms usually occur to protect some sort of injury...though you need not have had to actually injured yourself that you are aware of). It could be simply bending or twisting the wrong way, or picking something up incorrectly.
You mentioned you dont have any back problems, but have you ever had it checked by a doctor..or had any x-rays or mri's done? If you havent, then my advice is that you probably should, especially if it lasts more than a couple weeks and/or is starting to affect your daily lifestyle. Any time you have numbness with pins & needles is definitely nothing to fool with. Not to scare you, but it's better that you find out what is causing it when it's still early enough.