May i ask how long you have been feeling this way? Since "the sudden change"

This is a LONG reply, but i've experienced a similar thing, in a way, and i would like to share with you.

When i was younger (like in my childhood up to about age 13, i am 23 now) i was the complete opposite of how i am now. I was happy and bubbly and care free and didn't give 2 toots about what anyone thought about me. I suddenly started progressing pretty fast into depression and what seems to me every other related disorder under the sun and it has plagued me since. BUT, in the darkest point of my experience so far, before i got help, i experienced the same perverted pleasure from my negativity. I had very dark thoughts, and i thrived off my own negativity. I would push friends away in such a way that they saw me in the end as a complete nutjob...just to be absolutely miserable and feel like i have effed up, and ultimately enjoy it. Id think of morbid things and write morbid things and ....and somewhat enjoyed it. I would also dwell on things that hurt me, or heartbreak, and make effort to NOT get over it. I wanted to be in pain and have something to feel sorry for myself about. This went on for quite a while.

I eventually started getting into trying to figure out why i was that way, my ultimate theory was that it was some warped self destructive behavior. For me, personally, it made sense. I realised i actually liked myself and the way i was, but i also hated myself. There was this heavy ying and yang thing going on. . Now this sounds INSANE, i know. Almost sounds like i had 2 sides of me fighting each other for their reign over my mind and existence? Right?

I had a breakdown eventually, went insane and got checked into a clinic when i was about 17 where i had to see a psychologist everyday. She introduced me to the pretty simple theories of Carl Jung and how we all have our dark side and our light side, and typically the 2 should balance themselves out. Despite this dark issue i had with psychological and emotional "self destruction", i had always still had my better, lighter traits that would show face every now and again...In brief, we concluded that what i was experiencing was likely an insane clashing force between my light side and my dark side. I had major mood swings (still do). They were fighting for control over my mind. And the dark side used to often have more control over me. It sounds a bit like a split personality, but it isn't really.

I was told to recognize and split myself into my dark and my light, and give them each a name. I called my lighter side Shann and my darker side Shannon, and i was told to become aware of Shann and Shannon and how they were fighting one another to create an awareness and understanding.

This idea in my head and understanding has caused me to become better over time and learn to control my sides a bit better and make some peace between them to become more...neutral. I no longer have the same problem to that extent...but i still desire having the same problem just as bad as it was before. So the tension between my dark and light is still there, but i wont let them fight anymore. I do slip up and go through episodes, but I have somehow found a balance for the most part, for the better for myself and mostly for the people close to me

I hope that gives you something to think about and i hope you can relate in some way as i have related to you. Understanding is the first step to any cure (even if you dont want the cure )