Perhaps it was fatigue from the long journey.

Fatigue from physical exertion is a predisposing cause of heat-stroke, and constipation and alcoholic indulgence should be avoided.

While they took away the fatigue and gave her energy, she could think of nothing but chocolate sundaes and pickles.

Aside from fatigue, her body moved and felt the way it should.

The inference is that the "fatigue substances" generated in the muscle fibres in the course of their prolonged contraction injure and paralyse the motor end plates, which are places of synapsis between nerve cell and muscle cell, even earlier than they harm the contractility of the muscle fibres themselves.