I need to know if I have a possible mental disorder, please help?

Okay, a little about me, I suffer from diagnosed ADHD, OCD, SAD, an Anxiety disorder, Insomnia and Depression. In which I've stoppped taking medication and have been fine. Recently I lost a friend that I lived with due to immaturity and her stealing from me, so lately she's been getting her friends (as well as herself) to call me and message me, threatning me to a point I'm terrified to leave my house (Because I know these types of people) and saying shes coming after me and all that fun stuff. But now all I can think of is killing my "Friend" when I see her next. I honestly won't do anything to her cause I honestly couldn't hurt anyone. But I just keep thinking about it and finding great comfort in the imagery my head has created. I've become extremly apathetic and have started standing up for myself. My life is now more focused on revenge, and making her feel the way she's made me feel. I say once again I WILL NOT HURT HER, so this isn't a threat, I'm just concerned about why I'm thinking such morbid thoughts, and they are disturbing, every little detail is planned out in my head and sometimes it makes me sick. My heart feels like its going to explode from my chest and I can't stay still, I have like... the jitters or something. I'm quite scared but am not a risk to myself at all... I just need advice on if I have yet another mental disorder, going crazy or if theres anything I can do to gain a peace of mind... PLEASE HELP ME.