OK, Jean, derealization itself isn't directly "cured" by the use of antidepressants, but it is relieved by identifying and attending to its causes. Where, for instance, derealization arises in a context of episodes of severe anxiety, dealing with that underlying anxiety, whether by medications, or psychological methods, or both, usually relieves the derealization.
And rest assured, though derealization can be a very scary sensation, it is NOT the "beginning of madness". And if it were, uncommonly, to be related to an early psychotic illness, then again a proper assessment of the situation ought to identify that, and enable it, too, to be effectively treated.