Horrifying daydreams

So for as long as I can remember; I even have memories of this happening in elementary school. I've been having constant daydreams about doing things which I'll clearly never do because of my morals. They pop up out of nowhere; sometimes I'm happy and they come up and sometimes I'm sad and they come up. They always leave me feeling very stressed. I can always tell that they're just daydreams and that they don't affect me as a person, but they make me so nervous that during an episode I have to sit down because I don't have the energy to stand up and I have my heart racing. This has happened only a few times in public, and usually if it happens in public, people say that I look like I'm zoning out or something.

For example, many times the daydreams have involved me killing someone. After doing so, I start daydreamming about running away from the police and having the stress of gunshots getting fired at me. Then I start daydreaming about what being in jail forever is like. Then I start daydreaming about going all cold in jail and losing all of my emotions. Then I daydream about how all my friends look at me as a disappointment and tell me about how much potential I would have had if I were not in jail. And then finally the daydream leaves me to feel very anxious/depressed/unmotivated/angry and I feel awful. If I was doing something productive at the time, I stop doing it and listen to music or do something that will bring my spirits up.

The daydreams aren't always about murder--sometimes they involve theft or doing something legal but immoral like me telling someone who thought that they were close to me that I really hated them all along. They are often quite vivid in my head and I absolutely hate them because I'm constantly worried that this may become my future. Even though I know that I'm a motivated student with very good grades and great career goals I'm always worried that one day something will go wrong and I do something stupid and end up sacrificing my future.

I don't know why these things happen. I literally have a zero percent chance of doing anything bad. Okay maybe I've done some minor things but I don't think that I have the capability to kill someone; in fact, just the thought of killing someone in cold blood makes me want to throw up.

I'm really worried that somehow my friends will find out about what I've been thinking about and they'll tell me that I'm completely insane or I'm a freak or a psychopath or something and I'm really worried that