Swimming and playing volleyball at the beach can make you tired and pleasantly wiped out, but long hours filling and emptying a wheelbarrow of dirt on a hot day brings fatigue, a far more draining kind of exhaustion.
There is a noticeable difference between tiredness and fatigue. You can read a magazine or book before bed and get tired after a while, but if you work on math problems on a computer for a long time, you'll feel fatigue in your eyes, and maybe your brain will start to hurt. The Latin fatīgāre means to "tire out," "to fill to excess or to bursting." Even thinking about the Latin for fatigue brings some mental fatigue.