Trying to reduce Eliezer's emotional state to a single idea isn't going to be easy. Part of the reason is because he endures and experiences so many different emotional states in Night. Doing so reveals the true terror of the Holocaust and why it lies beyond any simplistic constructions of the good.
One element of Eliezer's emotional state is a sense of immeasurable sadness. Eliezer feels sadness at the fragmentation that the Holocaust brings with it. Gradually, Eliezer is broken from the elements that defined him. His emotional state of sadness is carved out by his separation from Sighet and his home and the destruction of his faith in the divine. It is also forged by his separation from his family, his division from himself as he is no longer a person, but merely "A- 7713" and eventually, his separation from his fellow human beings in the struggle for survival. Eliezer's emotional state of pain and hurt is the result of these experiences that seem to define different horrific elements within the Holocaust.
Another aspect of Eliezer's emotional state is anger. Eliezer processes what happens to him through a prism of anger. He is angry at the guards who push and prod him as he leaves Sighet, reflecting that it was at that moment that he learned to hate his tormentors. There is anger at the abuse he suffers at the hands of Franek and Idek. He also is angry at what the Nazis have done. When he witnesses the scene of terror at Auschwitz, Eliezer notes that he shall always remember the "moments that murdered my God and my soul and turned my dreams to ashes." Naturally, the tone of sadness is present. However, there is an undercurrent of anger that defines Eliezer's emotional state because of what the Holocaust did to his childhood and life. In this construction, it is clear that Eliezer's emotional state is complex and intricate.