Psalm 4:8 is David's resolution at the end of a day of trouble: "I will both lay me down in peace, and sleep: for thou, LORD, only makest me dwell in safety." The Hebrew word yachad — 'only' — is emphatic: God alone is the ground of safety, not circumstances, not locked doors, not resolved problems. The peace that allows sleep is not the peace of problems solved but the peace of God's presence known. This is the theological prescription for nighttime anxiety: not the resolution of fears but the anchor that holds regardless.
Psalm 91:5 addresses nighttime fear directly: "Thou shalt not be afraid for the terror by night; nor for the arrow that flieth by day." The Hebrew pachad — 'terror' — is the word for sudden, overwhelming fear. The promise is not that the terror feeling is illegitimate but that you are not obligated to obey it. God's protection is specifically named for the night, when fears are least manageable.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.