[tw1010]

Getting into a habit of exercise is the obvious answer. A less conventional advice that has sometimes worked for me is to totally embrace the feeling of being somber, and binge on some of the classic sort of miserable apathetic existentialist books. Things like Albert Camus' The Stranger, Sartre's Nausia, Beckett's Waiting for Godot, and Dostoyevsky's Notes from Underground. Sometimes after I have read those works, after I have stopped trying to ignore the feeling and just went all in for a few days, do I even get bored with being miserable and then start to look for other emotions to experience, and usually they're a lot happier in flavour. Obviously this advice could also exacerbate the problem, so try it at your own risk.