Perhaps Fantods is derived from Fantasym, or is perhaps is an abreviation of Fant-ode, fantasy song? (My folk etymology.)
**Fantasym is an unsettling jumbled and chaotic dream that we sometimes have upon waking up, with disconnected thoughts and images flying around. (Old meaning I think.)
A "fantasym" is the intense shudder of pleasure which a succubus or incubus experiences at culmination.
/humor
Regards,