Jesus was both totally man and totally God. He knew His flesh would suffer but most of all He knew he was going to take the sins of the world. At the cross He said Father why have You forsaken Me. It seems that while Jesus was taking the sins of the world the it caused a temporary separation between Him and His Father God. This was without any doubt the most terrible thing that could happen. Jesus had made the world with His Father as the Bible says in the Gospel of John Chapter 1 and many other places. Jesus had  never been separate from His Father in Their eternal heaven where time doesn’t exist. It had to be terrifying. I guess the closest thing we experience as humans is when we have to separate from someone we truly love and adore.