מדרש אויף תהילים 76:8

What does bakosharot (“prosperity”) imply? The one who is not pleased (with his mate) weeps, the one who is pleased sings. Hence the word bakosharot (from beki, “weeping,” and shirot, “songs”) is used in the text. He causes one to ascend the ladder and another to descend. Thus it is said: For God is judge; He putteth down this one, and lifteth up this one (Ps. 76:8).

Another matter, “it was at midnight” – this is analogous to a king whose province departed [from the norm] and imposed [unusually harsh] servitude on the captives that came to them, and [the king] too diverted the course of justice against [the officials of that province] and killed them. Similarly, Egypt departed [from the norm and] imposed [unusually harsh] edicts on Israel to work day and night, and by assigning man’s work to a woman, and woman’s work to a man. So, too, God diverted the course of justice against them and killed them at night, as it is stated: “It was at midnight.”²²Despite the fact that judgement in court, and executions, are generally carried out by day. Just as He overturned Sodom at night, so He killed the firstborn of Egypt at night. This is why David said: “You, You are awesome; who may stand before You when You are angry?” (Psalms 76:8).