He must have seen some monstrous apparitions that got him freaked out.

Wisdom of Solomon 17:15
Were partly vexed with monstrous apparitions, and partly fainted, their heart failing them: for a sudden fear, and not looked for, came upon them.
Isaiah 66:4
I also will choose their delusions, and will bring their fears upon them; because when I called, none did answer; when I spake, they did not hear: but they did evil before mine eyes, and chose that in which I delighted not.