Not to be blindingly obvious but: being in someone else's power and having none of my own. Though it depends on the situation. I didn't truly feel helpless when imprisoned by the Corps and in the reeducation center until the very end, when Department Sigma transfered me and some of the others to their authority, and then sold us out to the Shadows. Before, I was often angry, and sometimes very happy, occasionally for
the same reason, but I always had hope, and I never felt truly helpless.
Once the operations started - well, I wouldn't wish that on anyone. Not even on the bastards from Department Sigma, not anymore, though I wish I could give them an impression of it, just so that they know what they did to us. And then the machine in my mind, talking, demanding all the time. When I was last physically awake, in my own body, after we were rescued, it even made me shoot at people, including Al. I could have killed him, and would have been unable to stop myself. One more reason why I can't permit anyone to stop the cyrogenic sleep before the implants aren't removed.
Least vulnerable: There is no such thing as complete safety, but I'm glad for my additional training with Varzil and the others. Not just because of the honing of my abilities - actually that's the least of the reasons. Being able to communicate with people again, being able to help others instead of being passive and useless, or wandering through the systems - that makes me feel stronger. That and the knowledge that I can still feel. They didn't take this away from me. I'm not a drone. I am. And even if I should die, which is a possibility because I made Michael promise he'd pull the plug on me if there is no possibility to remove the implants, I was.