Well just know you aren't alone in this, I'd hesitate to say it is fairly common. I sometimes find myself laughing at really gruesome stuff and stories. It's just a healthy amount of schadenfreude, pleasure derived from the pain of others. Wikipedia says children and adults get it, just adults are better at hiding it normally. So maybe you just derive more immediate pleasure, that's no big deal really. And you recognize that it's wrong or you want to feel something else so you've got nothing to worry about at all. It's just a bit of a primal part in all of us, don't worry about it at all