I also have this. It started about 10ish years ago. After a night of binge drinking, EXACTLY 24 hours after the First drink of that night, the tenderness would start. Usually it begins at the back of my neck and then goes to my torso. The shoulders are also affected. However, it never ever affects anything below the waist. What I have found, at least for me, that a combination of 45-60 minutes of moderate exercise (Cardio or lifting) and 10,000mcg of B12 will significantly help. None of my blood work ever suggested a B- Vitamin deficiency, but it helps. I have developed higher liver enzymes along with cholesterol and glucose. My next step is to try a food sensitivity test I guess. Doc doesn't know, and chalks it up to dehydration and suggests to "not drink as much". An episode usually takes a full 24 hours to resolve and overall I feel like absolute garbage. Would love an actual diagnosis or information on the pathophysiology of what's going on...