One should always consider a pre-diabetic state, or insulin resistance. This is not a simple thing. When glucose cannot get into the muscles' cells, they simply don't work either! The brain suffers too. Weakness, and shaking, central fatigue states can confound other conditions present.

Since there is an epidemic now of type II diabetes, often starting in teenage years now...it is something to always watch out for.

When people have so called "normal" glucose tests, like fasting or short GTTs...they may in fact be already impaired. Peripheral neuropathy may begin then. Nerve damage is nerve damage, and a person can have more than one cause going on.
Nerves need glucose too to function.

This is so common now... we get many YOUNG people on our PN board now, and in the past that was never the case!

It is always a good idea to keep an open mind about a severe diagnosis...other things can happen concurrently.