פירוש על סוכה 51:21

In R.Shila's name they said "a groom is exempt"- from reading Shema because (he is) preoccupied and other members of the wedding party are obligated. These Tannaim (of this Braitta) do not hold "one who is involved in a Mitzvah is exempt from another Mitzvah".

One who is in discomfort. When the Sukkah is discomforting him.