Stalling the horizontal stabilizer can happen in icing conditions where leading edge ice causes the airflow to separate at a less negative AoA than normal. What isn't intuitive is that the recovery procedure is to pull back on the yoke, rather than pushing forward like a stall of the main wing. The reason is that the tailplane is at a larger negative AoA when the main wing is at a smaller AoA (faster), and vice versa. To reduce the negative AoA on the horizontal stabilizer, you must increase the AoA on the main wing. The reason should be clear if you view the orientation of the horizontal stabilizer to the relative wind in each of the two situations, being fast and being slow: A critical piece of information for interpreting the above diagram is that the AoA on an airfoil is normally measured as the angle between the relative wind and the chordline of the unaugmented airfoil, meaning no flaps, and the elevator (and rudder, ailerons) are simply plain flaps. So deflecting the elevator by definition has no effect on the location on the chordline.