Today's daf contains the complicated topic of when one involved in a mitzva is exempt from Shema. Within this discussion, the Gemara deduces that a Chatan on his wedding night if he is marrying a Betula is exempt from the Shema because he is טריד, usually translated as burdened or agitated, with the burden of the mitzva he is about to perform. The Gemara contrasts this with a person whose ship has sunk at sea or a person in Aveilut, mourning, who is burdened and yet is obligated to say Shema anyways since the burden is not a burden brought about due to a mitzva.
This distinction between the mourner who is טריד and the Chatan on his wedding night who is טריד has always puzzled me. Isn't the mourner also burdened due to a mitzva, namely the mitzva of Aveilut, so shouldn't he ALSO be exempt from Shema like the Chatan? I looked through many Rishonim and Acharonim to see if they address this question and have yet to find one who does. Am I missing something obvious here?
The closest anyone comes to dealing with this question is the פני יהושע who points out that the fact that the verse excluded the mourner on the first day of mourning specifically from the mitzva of Tefillin indicates that he is obligated in all of the other mitzvot. However, this seems like circular reasoning to me when applied to my question. The mourner is obligated in Shema because the Torah did not specifically say he is exempt? Maybe it was obvious that the mourner should be exempt from Shema based on the same logic as the Chatan on the night of his wedding to a Betula! Namely, that he is burdened and the burden is a mitzva burden, the mitzva of mourning, and not a רשות, a non-mitzva burden, like the one who is bothered by the fact his ship has sunk in the sea! I would appreciate anyone who could provide me with an answer to tis question (in the comments below or on Twitter) or at least point me in the right direction.