of course. self-regulation is helpful because "normal people" fluctuate in terms of their moods, behaviors, etc. it's the normal ups and downs, and the "sanity" of a person is not only determined by their moods and behaviors, but also by what the person does in response to those. for example, many mental "illnesses" are diagnosed on the basis of not having enough self-control. many problems come from not being able to control yourself, and not being able to recognize that other people deserve respect, privacy, happiness, etc.
what i am saying is that questioning your sanity is a form of regulating yourself, in terms of your behavior, self-image, your reputation with others, and so on.
of course, clinical depression and many other conditions cannot be helped. however, my point is that, in the course of regulating yourself and trying to actively be normal, you may question your own sanity. am i going crazy? why did i just obsess over that person, or thing, for so long? is there something really wrong with me? they're all normal questions, and just because you ask them does not mean that they are true. unfortunately, sanity and insanity are not so clear cut in terms of lines and boundaries, although there must be lines for diagnosis' sake. the way i see it, there are two extremes to every behavior and its opposite. normal is when you're somewhere relatively around the middle, and you get diagnosed for something if you are too far away. there's no real line, so clinical practitioners draw that line for us on the basis of whether or not it is harming us and harming others. we all have our own idiosyncrasies, and to be honest if other people knew what we did 24/7 our whole lives we would probably look insane.