You were Infested by the Zerg quite a bit back, and Artanis was going on a manhunt to find you, until he finally did. He sent some Dark Templars to tranquilize and subdue you before bringing you to the ship. And once they did, they brought you to a containment cell before strapping you down on an operating table to have you Deinfested. Artanis insisted on doing it himself, as he wanted to see his friend being helped instead of standing idlely

"Do not worry, my friend... I shall help you.... Just hold still..."