According to Moshe, in the Book of Exodus Chapter 10:21-29, the Egyptians underwent darkness for 3 days where they did not move. Solomon in the Book of the Wisdom of Solomon gives us more detail of what was going on in that darkness. He said that the Egyptians could not sleep (or intolerable sleep) during this darkness because they were seeing monstrous apparitions. Y’all, the Egyptians were seeing demons! The word monstrous means frightening, huge, evil, unnatural or horrifying. The word apparition means spirit or manifestation. From The Wisdom of Solomon Chapter 17:14-15. Solomon said something else that was interesting. He said that the Israylites could hear them in their darkness. Chapter 18:1. They were probably screaming and/or crying at the form of those demons.
You might ask, well if it was so dark how could the Egyptians see those demons? Not to long ago, I was watching this paranormal show. This man that had a demon(s) in his house said something that I found very interesting. He said his room would be totally dark yet he could see this demon in his bedroom and that the demon WAS DARKER THAN THE DARK IN HIS BEDROOM! He could see its form. Anyway, Solomon also said the same thing that Moshe said, that the Israylites had light and were happy (in Goshen).
An interesting statement Solomon made in Chapter 18:2 was that Ysrayl did not seek revenge on the Egyptians when they were in total darkness. They certainly could have wiped them out but they did not. Why? Because this was the ninth plague (Yah had one more plague to go) and vengeance belonged to Yah. The Israylites let Yah show His hand, they waited on Yah.
*I forgot to add that Solomon said that the magicians of Egypt were very terrified during this darkness. Remember, they came up against Moshe after he turned his walking stick into a snake(s).