Question
My ego is bothering me with a question that I cannot answer, is something like this: How the perfect mind of the Son of God could have this crazy idea that he could be separated from God and have his own world?
I think Jesus says in some place on the Text that is the same thought we are having now, if we see the world is because we still believe the same crazy idea, even thought it was corrected by God the same instant that occurred.
But if the mind of the Son of God, could have that crazy idea, why He cannot have another one, and then another and so on?
Sorry if seems a silly question for you all, but is really bothering me.

Answer
Actually it is among the most common asked questions, and that is why Ken and Gloria answered it in their book. "The Most Commonly Asked Question about ACIM" So it is not silly at all, even though you might not like the answer which is given below. 

Chapter 2: The Nature of the Separation.
11) How did the ego originate, and what is to prevent the separation from happening again?

This is unquestionably the most frequently asked question of all, and it seems as if every student of A Course in Miracles has wondered about this at one time or another. We have been impressed over the years by the ingenuity with which Course students have framed this question in many different forms; yet the basic question itself can be restated in this way: "If God is perfect and unified, and has a perfect and unified Son, how could an imperfect thought of separation and division have possibly arisen within such a Mind?"'

Jesus' answer to this question in the Course comes within a non-dualistic framework, and will hardly satisfy an intellectually inquisitive mind that demands an answer on its own terms. However, within the dualistic framework that we experience as our reality, the question is really a statement masquerading in question form, "asked" by an ego mind in order to establish its own reality and unique identity. Therefore, the questioner is really saying: "I believe I am here, and now I want you to explain to me how I got here."

Consciousness, being the first split introduced into the mind of the dreaming Son, is an ego state where a perceiver and a perceived seem to exist as separate "realities." Consciousness results in a concept of a limited false self that is separate and uncertain, seeming to experience an opposite to the true Self as God created It. And it is this false self that believes it is "here" and "asks" the question about its own seeming origin, thereby seeking to verify it. In truth, however, imperfection cannot emanate from perfection, and an imperfect thought of separation and division cannot arise from the perfect Mind of God's perfect Son, in which opposites cannot exist. Only in a world of dreams can these absurdities, and the beliefs that foster such uncertainty lead to musings like this.

The question therefore can only be asked by those who believe and experience that they are indeed separate and distinct, and it can only be answered by someone who agrees with this premise that the impossible has in fact happened, and therefore requires and even demands an explanation. Thus, only a dreaming ego would ask such a question, since a Son of God, certain of his Identity in Heaven and awake in God, could not even conceive of the separation which is the basis for asking the question in the first place. And obviously, if in reality the separation never happened once, how could it possibly happen a second time? Therefore, once again, it is a trick question, much like the comedian's question, "When did you stop beating your wife?" which, if answered, can only incriminate the person responding.

Jesus directly addresses this question two times: The first is found in the text, where he gives a very practical answer to what was originally a question posed by William Thetford, Helen's colleague and friend, as she was taking down the dictation:

  It is reasonable to ask how the mind could ever have made the ego. In fact, it is the best question you could ask, There is, however, no point in giving an answer in terms of the past because the past does not matter, and history would not exist if the same errors were not being repeated in the present (T-4.II.1:1-3).
In other words, why worry about how and why the separation happened in the distant past, when you are still making the same choice to be separate in the present?
The next answer comes in two parts, and is found in the clarification of terms, the appendix to the manual for teachers. Here, Jesus' answer is much more to the point as it addresses the pseudo-nature of the question itself, and his answer is reflected in our discussion above:

  The ego will demand many answers that this course does not give. It does not recognize as questions the mere form of a question to which an answer is impossible. The ego may ask, "How did the impossible occur?", "To what did the impossible happen?", and may ask this in many forms. Yet there is no answer; only an experience. Seek only this, and do not let theology delay you (C-in.4).
  Who asks you to define the ego and explain how it arose can be but he who thinks it real, and seeks by definition to ensure that its illusive nature is concealed behind the words that seem to make it so.

  There is no definition for a lie that serves to make it true (C-2.2:5-3: 1).

Reproduced with the kind permission of Gloria and Kenneth Wapnick and the Foundation for A Course in Miracles®