I have a tendency to go in and out of depression. I can spend days, weeks or months at a time completely happy, but eventually I swing the other way and feel overwhelmed, lost, sometimes alone and existentially surreal.
During the former mindset, I sometimes drink alone because I have appreciation for good wines, craft beers, aged scotch and various liqueurs. You don't have to get drunk to enjoy these things. Hell, you don't even have to get drunk with friends. A little alcohol will loosen your inhibitions and make lots of activities, be it alone or not, a lot more enjoyable.
During the latter mindset, I waste a lot of expensive alcohol that I otherwise enjoy in moderation because it makes me feel numb, which is a far better feeling than not understanding how or why you feel the way you do. It does occur to me that this is probably the result of psychological illness, I just can't be fucked to do anything about it. Too much to do, too much to learn.