The Torah forbids us to harm ourselves in any way when mourning over the dead because we are a Holy nation. לֹא תִתְגֹּדְדוּ וְלֹא תָשִׂימוּ קָרְחָה בֵּין עֵינֵיכֶם לָמֵת כִּי עַם קָדוֹשׁ אַתָּה לַיהוָה אֱלֹהֶיךָ (Re'eh 14:1-2). The Netziv says as follows regarding this pasuk.
"You need to know that any pain or bad thing that happens r"l is the will of Hashem and done for His honor or to forgive your sins which is also His honor. It is befitting of a people who are Hashem's people to nullify their pain in the face of Hashem's will. However crying and mourning over the dead in the measure that the Torah prescribes is the will of Hashem to honor the dead. We see that honoring the dead takes precedence over other mitzvos of the Torah."
This Netziv clearly says that a person cannot be sad or grieve over his bitter plight for any reason whatsoever. The only time a person can grieve is for the dead, but not because it is such a severe blow that we allow our human emotions some leeway. Our emotions are never allowed to overtake us. Only Kavod and Ratzon Hashem.