What does Boxing Day have to do with boxing?
"the state of an animal when it is feigning death," 1883, from German kataplexie, from Greek kataplexis "stupefaction, amazement, consternation," from kataplessein "to strike down" (with fear, etc.), from kata- "down" (see cata-) + plessein "to strike, hit," from PIE *plak- (2) "to strike" (see plague (n.)). Related: Cataplectic.
cataplexy cat·a·plex·y (kāt'ə-plěk'sē)
A sudden loss of muscle tone and strength, usually caused by an intense emotional stimulus.