Let's talk about functions and opposites a little:
According to type theory, we somehow differentiate our dominant functions (through nurture, nature, a combo, whatever) -- and we make them dominant. We pick 2 out of 8. While we do this, we also give rise to their opposite. White does not exist without black, light without dark, right without left. The good news is, both of the opposite functions can be utilized in the service of #1 and #2, if concious effort is spent on using them this way.
However, if a person is tired, stressed, feels his dominant functions "failed" him, then tertiary and inferior funcs can subconciously take over; in these cases, they will cause episode resulting a person feeling as "not acting himself"; an almost Jekyll and Hyde scenario.
For example for an ESTP, tertiary and inferior are Fe, Ni, the latter being the inferior. Ni is about projecting, about future possibilities, but in the negative, in environments which a lot of future goals are discussed can provoke an inferior experience for ESTPs. Also as a rule, if any of the lower tier functions are activated, it usually means the other comes to play as well, so the whole thing feeds on itself -- for ESTP Ni can bring in Fe -in its negative form- which, in general, handles connecting to other people, but this time it will project animosity.
Functions in their negative forms are just weird. For example Ni in the weak form will attribute meaning to isolated minor incidences that are not there. Dominant Ni can make inferences, but in the negative the conclusions they draw will often be quite off the mark. A "message" is read into a friend’s request to borrow a car; or a wife coming home later than usual arouses suspicion, a song popping into an this person's head might be taken to mean that her supervisor is angry. The smallest thing builds up to become a huge problem. Such people while "in the grip" as Naomi Quenk calls in her book Was That Really Me? can seem quite pathalogical.
Jung (who provided the basis of much of MBTI) says:
The inferior function is always associated with an archaic personality in ourselves; in the inferior function we are all primitives. In our differentiated functions we are civilized and we are supposed to have free will; but there is no such thing as free will when it comes to the inferior function. There we have an open wound, or at least an open door through which anything might enter.So if you cannot profile using dominants, go to tertiary and auxilary.