In this video, C.G.P. Grey explains what a nocebo is. Yes, it's quite similar to a placebo, but, you know, not good. Have a look:
For further reading, Grey includes a list of citations in his YouTube video description, and there's an official discussion thread on Reddit.
Chris Higgins is the author of The Blogger Abides, and has written for This American Life, The Atlantic, Breakfast on Mars, and The Magazine. You can follow his adventures on chrishiggins.com.
View the discussion thread.