I have severe SFN and LFN, as a result of CMT (hereditary sensorimotor neuropathy). With almost no sensory feeling left in my feet and legs distinguishing between the two is difficult, but I assume the burning and stinging pain is caused by the SFN. The strong, sharp pains in my legs and the constant ache is probably from the weakened muscles trying to carry the load. I have visible muscle wasting, but this is from a long standing disease process from childhood.
I am also one of the people here with all over body burning. I am currently having a flare of this, just sitting or lying down is uncomfortable - contact with the furniture burns, even if I put a soft blanket down, most of my clothes burn my skin, and my hands lying in my lap or one leg touching the other hurts. It is very distracting and uncomfortable, even painful to the point of making me pace the floor. Having constant consciousness of all over skin burning is a crazy-making situation, I do understand.
The first time this happened I told the doctor and we tried withdrawing my opiates, which had no effect on the burning but pushed the pain and sleeplessness through the roof. Then we thought it might be changing gabpentin manufacturers. Nothing made any difference. After a few months the burning contracted to my left thigh which has remained extremely sensitive. This pattern repeats every so often. I am not sure if it is affected by the weather or hormones, but it is particularly bad this time. I do not believe there is any treatment beyond trying to make yourself as comfortable as possible, choosing clothes with care, and keeping cool. I do find that if I get warm it is worse. It has lasted for several months at a time.
I believe this to be a symptom of SFN.