opisthotonos
Sustained tetanic spasm in which the body is bent backwards and stiffened, as produced by various diseases.
uncountable
[T]he Actors struggled & bounced, and sprunted as if in Convulsions; like Patients under the Influence of a Disease called in Jamaica the Opisthotonos or dry Gripes […].
Where it comes from
From Latin opisthotonus, and its source, Ancient Greek ὀπισθότονος (opisthótonos), corresponding to opistho- + tonus (“muscle tension”).
Adapted from the Wiktionary entry opisthotonos (CC BY-SA 4.0).