三昧 (sanmai) is the Japanese transliteration of the Sanskrit word समाधि (Samādhi), which is a state of deep meditation. I believe that "fera-sanmai" ("fellatio-samādhi") would refer to that state of being entranced or utterly carried away by the pleasure of being sucked off, which is a frequent feature of much Japanese porn, both that involving females and males, or that involving just males.