how would you explain the ups and downs in Walter's moods?

Walter has big ups and big downs. It looks like Walter may have a mood disorder like bi-polar depression but mental illness was largely not something dealt with at the time. Consider when Walter walks into the apartment drunk but instinctively starts dancing along with his sister, loving the beat of the drum in the music. During this scene, the inebriated Walter begins to act out a scene in which he is the chief of a tribe. He prepares his imaginary tribe for war by invoking war songs and the songs of his ancestors. At the best of times Walter is an intense man with nervous movements and erratic speaking patterns.