I've never used ketamine, but I did take hallucinogenic doses of dextromethorphan (DXM, a dissociative hallucinogen, the same class of drugs as ketamine) a few times in college. I have mild depression, and for several days to a week after each DXM trip, I felt very energized and creative, with all of my depressive symptoms gone. I'm not surprised that ketamine helps depression in some people. I sometimes consider microdosing DXM for depression and also general productivity.

Of course, don't take any medical advice from anonymous online posts.