Ah yes, many muslims and christians disagree on this point.
First you have to understand that Christians believe that God exists in three characters. Like an egg has the shell, the white and the yolk and that is what an egg is. You can not have one without all three. In the same way we believe that There is The Father, The Son (Jesus, who walked in the World) and the Holy Spirit (who guides us while we can not physically be with God.)
Jesus is referred to as the Son of Man because His mother was human. His mother became pregnant by the power of God (not by sleeping with anyone.) So he was both the Son of Man and God in flesh.
I don't know if you understood what I am trying to say because I am not good with words. If you want I can find the scriptures that explain what I'm trying to say.
You would also know that lying prostrate is the form of complete respect. Jesus was trying to show that He was willing to take His father's plan above anything else and respected/loved Him more than anything. Islam respects Allah above all and you lie prostrate to him out of complete respect and honour.
I hope my answers gave some explanation which is not too confusing to understand. I will be to answer any more questions you have.
I am sorry that my answer is so long, I did not mean to write an essay lol.