Hi-This may be totally unrelated but I too, post Moderna vaccine experienced extreme sunburn like burning in the opposite arm from where I received the injection, but is an arm where I had nose removal from breast cancer in 2016. That said, it happened upon awaking and within seconds I had extreme and random nerve firings throughout my body from the back of my neck all the way down to the bottoms of my feet that lasted for days - the head was spared and the burning arm resolved about 30 min later? This was considered an adverse reaction and I subsequently got the Pfizer vaccine that has 2x less the mRNA that my immunologist told me. Given my reaction I didn’t want to get a second shot but she said given my response and probably a result of my Mast Cell Activation Syndrome I should get the vaccine. I got the Pfizer without issue. I have faulty collagen/connective tissue (hEDS) and crudely explained mast cells in those tissue may be disruptive or even have extra amounts and reside close to the nerves - therefore I believe my predisposition with Mast Cell Activation Syndrome (an extreme histamine intolerance type condition again explaining crudely here) caused the flare of nerve pain burning sensation in my weaker arm. Additionally, I have hyperadrenic POTs (over production of adrenaline and a comorbidity often with both hEDS and MCAS) that can trigger a mast cell reaction as well I recently learned. Also, I l’ve come to understand that when we awake our bodies naturally release this adrenaline hormone as apart of the awakening process. Therefore, I assume why I feel internal tremors occasionally when awakening and lying in bed, as well as tingling sometimes and most likely the sunburn feeling I had lost vaccination. This may NOT have any relevance here but sharing in case any part of this may resonate with you. I hope you reach a diagnose and treatment soon! My migraine Dr referred me to a cardiologist who did a tilt table test that revealed I have a rare subtype of POTS and the recommendation to calm this over activation in the body and heart rate is to take beta blockers. I share all of this as it’s through forums I gleaned insight to my own undiagnosed treatments at that point in time. I wonder if CBD cream may help reduce your pain? I’m allergic to Motrin and most drugs (even had to go off my cancer drug) and have joint and muscle pain and my cousin sent me some amazing CBD cream (not sure if I’m able to mention the company here but happy to if given the green light) and much to my surprise within 10-15 mins I became pain free Best of luck! hEDStong.