He sounds very unhealthy. Is he a good friend? If not, I’d probably disengage.

If he has a problem with alcohol he is self medicating with a depressant that he turned to possibly deal with anxiety issues possibly an escape from feeling due to possible trauma he experienced. People with this challenge experience highs and lows mood swings and tend to lack in normal adult problem solving skills. And they can act impulsive and have anger out bursts even rage ranting episodes

It can feel like you are dealing with someone that has more than one personality. Some have mentioned a doctor Jeckle and Mr Hyde and the euphoric third personality as well.