I Noticed A Few Days Ago That Towards The End

I noticed a few days ago that towards the end of my work day that my leg will start shaking pretty bad when i extend and use my muscles applying pressure, like pushing on the car brake. I work outside and try to stay hydrated, i have had a harder then normal work week. I am supposed to have neck surgery soon because of a damaged nerve in c6 of spinal area, can this be the cause of this or is it simply dehydration and fatigue?