My husband was mowing and suddenly his body shakes and he feel tired can't stand for long?

Could be heat: If he were working in heat and started to chill or quit sweating i would think heat injury. I would also be concerned about sugar. If it came suddenly there is less chance of it being a hidden illness like ms. Strokes usually affect one body side.

Shaking: If he still having problems he needs to see his primary care doctor. He may have been dehydrated of it was hot outside.