I think most people with mental illness question the 'reality' of their illness at one time or another. Its so hard when you cannot look down and see your arm rotting off or look at xrays and see the broken bone...mental issues are entirely up to your ability to report them and I think its in our nature to question ourselves; part of the illness. I cannot imagine why someone without problems would pretend to have them. I know your pdoc seems to be a jerk, but I cannot imagine she is really trying to out you or anything like that. And I don't think she can just give you a placebo without your permission. I'm fairly certain you have to sign all kinds of paperwork and be told that you will be experimented on to have someone replace your meds with a placebo.

I've personally had this problem before (well not with lithium, but with my meds in general). I have felt certain that I'm a big *** faker, making it all up, making my life harder for no reason and my pdoc, husband, everyone was just humoring me and my pdoc was just giving me sugar pills to keep me quite and happy.

In retrospect I can see that I was being ultra paranoid during these times, but I tend to have problems with paranoia in general. To ease your worries, why don't you either call the doc and tell her you are coming to pick up a copy of your lab report, or call the lab and tell them. Give them a few hours and then go get the report. Perhaps with your hand on it, you will feel better?