The verb occurs as e)gkoisuro/omai in classical Greek; its locus classicus is Aristophanes, Clouds 48 (web address 1), and it is glossed in LSJ s.v. as "to be luxurious as Coesyra (a female name in the Alcmaeonid family)" (cf. kappa 2568 on Coesyra). The form appears in Aristophanes as the perfect passive participle e)gkekoisurwme/nhn; the form is accordingly presented here in the perfect passive infinitive, as a citation form.
The verb on its own appears in Hesychius, the scholiasts, ps.-Zonaras, and Gennadius Scholarius' Grammar, with similar glosses -- though ps.-Zonaras misconstrues it, with some folk etymology, as "dragging oneself out of bed" (e)k th=s koi/ths su/resqai) A couple of late Byzantine authors use the verb on its own: Manuel Philes (C13-14) Poems 5.15.6; Mazaris (C15) Journey to Hell 1.30.18, 1.42.12.