Is it normal to fantasize about mutilating oneself and others?

I promise this is probably not as bad as it seems. Often times while I'm trying to focus on work, I'll drift off and zone out, then start thinking about all the ways I could kill myself and others utilizing the objects around me. The sensation is sorta like daydreaming, only more cynical. I have been diagnosed with depression (the kind your genes give you, not a short-term episode) and I know I may also have some sort of focusing or learning disorder, either of which could be the cause. Whatever the case, people often find this shocking and disturbing, and I wanted to know what this little community had to think about it.