Daniel 10:2 Kabbalah

בַּיָּמִ֖ים הָהֵ֑ם אֲנִ֤י דָֽנִיֵּאל֙ הָיִ֣יתִי מִתְאַבֵּ֔ל שְׁלֹשָׁ֥ה שָׁבֻעִ֖ים יָמִֽים׃

In those days I Daniel was mourning three whole weeks.

Read kabbalistic (mystical) interpretation of Daniel 10:2: and classical mystical sources.