Weed whacker will sure do it. I had a couple of places I mowed where the weed whacking took longer than the mowing. After half a day holding onto a vibrating weed whacker, I couldn't hold eating utensils or a glass w/o shaking like a leaf in a wind storm.
That's probably it, not certain why it's never happened before. I was having trouble holding things last night, seems to be getting a little better.