Self-experimentation is causal inference with a sample size of 1 and selection bias, e.g. silly and doomed.
Self-experimentation with within-subject design can be internally valid (I make sure mine are well-powered, even, which is more than some psychologists can say), but this does nothing about external validity or selection bias.
Which ironically makes self-experimentation somewhat analogous to quantum suicide experiments: because of selection bias, observers of my self-experiments will rationally learn little even as I learn much more. Someone watching quantum suicides will expect to see lots of survivals, and someone watching self-experiments will expect to ...
http://www.johndcook.com/blog/2013/02/04/four-hours-of-concentration/
And since this is the Internet, and facts are involved, our gwern turns up there also.