מַה־תִּשְׁתּ֬וֹחֲחִ֨י ׀ נַפְשִׁי֮ וַתֶּהֱמִ֪י עָ֫לָ֥י הוֹחִ֣ילִי לֵֽ֭אלֹהִים כִּי־ע֥וֹד אוֹדֶ֗נּוּ יְשׁוּע֥וֹת פָּנָֽיו׃
Why art thou cast down, O my soul? And why moanest thou within me? Hope thou in God; for I shall yet praise Him for the salvation of His countenance.
Rashi on Psalms
are you downcast Heb. תשתוחחי, an expression of (below 44:26): “For our soul is cast down (שחה) to the dust.” When שַּׁח is used in the reflexive (מתפעל), the “tav” separates the radicals in the manner of every word whose root begins with “shin.”