כל ימי הייתי מצטער

After an intensive amount of internal polling (on the heels of this) it transpires that a statistically significant number of people do not see the analogue, and that they are likely to persist with an enduring dubiousness on the matter. What follows is a quick attempt to clarify and hone the subject:

The Lubavitcher Rebbe's concept ofמצטער  as applicable to someone with mental anguish engenders two discrete responses:

1) A 'Mitnaged': This is absolutely ridiculous. No such Halachic concept exists.

2) A 'Chassid': Who are we kidding, nobody is actually bothered to such an extent.

The difference between these reactions is global, nay, cosmic; the first acknowledges the כמות, the 'quantity' of anguish, but merely is of the belief that its איכות, its quality, is insufficiently meaningful (or, extraordinarily absurd) in respect to צער. Whereas the second is amenable to the איכות, the general concept of acknowledging such pain, but conversely is unconvinced that most possess the appropriate amount, the כמות, of צער necessary to impact the law.

Both can find a parallel -- and an answer -- in the supplied responsum.

The 'mitnaged' is immediately persuaded to abandon the tack of mockery he has adapted, as such an approach can no longer be classified as "the Lubavitcher מצטער".

The 'Chassid' too can reevaluate his own definition of צער; most initiate the topic with the assumption that an acute sense of pain must immediately overcome a person who is described as מצטער. But R. Shimon's language [אם יאכל מצה, כל היום עולים בלבו הרהורים וירא אולי לא היו כשרים כראוי ולבו נוקפו מזה כל היום ומצטער על ידי זה מחמת ספיקתו] indicates that he is referring to agony experienced subsequent to the "transgression". The pain in question then is namely, the feeling of dread and horror in response to discovering that a major sin was inadvertently committed (think any Kashrus scandal) which is universal. Personal opinions may vary on what constitutes sin, but the reaction to one's perceived iniquity is equal in all who experience it.

Thus, R. Shimon indeed wasn't arguing that everyone undergoes post-Matza stress symptoms. However, he maintained that deference should be paid to those who do, and that such people should be allowed to take their feelings into account in advance hence ensuring their עונג יום טוב. Similarly, the Lubavitcher Rebbe didn't claim that beingמצטער  in a Succa was guaranteed and reflexive; what he did state was that there are many Chassidim who would take this matter so seriously (either due to personal Yiras Shamayim [= concern about the presence of אורות המקיפים דבינה] or Yiras Rabbo [= the insistence on abiding by every assertion of the 'Mitteler Rebbe', or his own Rebbe for that matter]) that should they awake with a start and determine that they had indeed unwittingly slept within a Succa, this would be a genuine cause of great distress. Knowing this in advance, the Rebbe maintained, was sufficient grounds for applying the rule of מצטער in a practical fashion.

So, in sum, the Rebbe did not invent a new מצטער; rather, he took a familiar feeling and readapted it as applicable to דירה and צער.