M’nos HaLevi writes that Esther was distressed because Mordechai chose not to tell her the reason for his behavior, himself.
The Talmud (Megillah 15a) takes the unusual word, “vatis’chal’chal” (“and she was distressed”) literally as “became empty.” In other words, the Talmud says that, upon learning this news, Esther either became a niddah (began menstruating) or had loosened bowels. In other words, as Rabbi Mendel Weinbach puts it, the news for Esther was so intense, that she lost control of her physical functions.
The Midrash (Esther Rabbah 8:3) similarly says that Esther miscarried at the news of Mordechai’s mourning. Torah Temimah says the Midrash here is using the root of the word, “chalal” (“empty”) to refer to the last chapter in Yeshaya (66:8) where the prophet says that Tzion will have troubles (“kee chala gam yalda”), and will give birth, indicating a relationship between this word and childbearing.