It could be a vitamin B deficiency...B complex feeds the nerves...most of us are deficient in B vitamins.
We get them from carob, brewer's yeast, raw whole grains...so you see why we can be deficient?
I suggest that you get a B 100 complex vitamin and take it every day. It is water soluable and is not toxic, as what you don't use will wash out of the body.
Drink lots of water, too.
The B adds a dark yellow color to the urine. it is harmless.
__________________ Tree Frog