אֲנִ֥י שָׁכַ֗בְתִּי וָֽאִ֫ישָׁ֥נָה הֱקִיצ֑וֹתִי כִּ֖י יְהוָ֣ה יִסְמְכֵֽנִי׃
איך לײג זיך און שלאָף אײַן, איך װאַך אױף, װײַל גאָט לענט מיך אונטער.
Radak
I laid me down and slept: – I laid me down in safety and slept in peace as a man free from fear.
Ibn Ezra
I (אֲנִי - ani): Securely I will lie down and sleep (ashkevah ve-ishan) during the night that was [just before or just after] the morrow of the battle. And some say (v'yesh omrim) [interpreting allegorically]: That when a person's mazal (fortune/destiny) falls, he is comparable to one sleeping (yashen). And when the mazal awakens to benefit him, he is comparable to one waking up (mekitz).
Rashi
I awoke from my worry, because I trusted that the Lord would support me.