I don't understand your hypothetical. Could you give a concrete example?
http://www.maths.bris.ac.uk/~maxvd/didelez_etal_StatSci_final.pdf
With repeated measures design the problem is whether the "washout period" is sufficient.
http://www.maths.bris.ac.uk/~maxvd/didelez_etal_StatSci_final.pdf
20 pages of theorems on do-calculus is not helpful, and the examples they use like retrospective pregnancies or case-control studies do not seem to apply to self-experiments.
Maybe I should be clearer: can you give an example of a real self-experiment, preferably one which was done blind & randomized, which is plausibly affected by your selection bias? Because I still don't understand what you are getting at.
...With repeated measures design the problem is whether the "washout period
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.