Body temperature varies over a 24-hour period, with a low point roughly between 4 a  m  and 5 a  m  Speed of reaction varies in line with body temperature, such that whenever body temperature is low, speed of reaction is low  If low body temperature caused slow reaction, the speed of reaction should increase if we artificially raised body temperature during the period 4 a  m  to 5 a  m
But the speed of reaction does not increase
Low speeds of reaction do not cause low body temperature.