Luke Skywalker spent virtually the entire movie in post-crisis shock. He was in a life-or-death situation right up until the conclusion of the Battle of Yavin. He had literally NO TIME TO PROCESS what was going on. This is not in any way incredible. This is rather normal and common.
I think, offscreen, about 20 minutes after the little medal giving ceremony, he probably had a nervous breakdown and needed inpatient psychotherapy.