When I read what you write, I think you are a kind and good person, that might have been severely traumatized by something and might be experiencing intrusive or delusional thoughts due to what had happened to you. It’s fine if you don’t feel this way. My advice would be to try to get professional help. People usually don’t get why someone can’t undo a thought or push it away, because they had either an easier time overcoming trauma or haven’t had a trauma in this lifetime. It is true that thinking positive might be beneficial, but trauma makes that hard. You need first to reprocess the image that causes the most trauma and stress. And them you need to pick another trauma experience and reprocess that. Until you have had like 7 or 10 images. It’s very difficult to do this on your own, hence why I advice you to get professional help.
If you can’t get help, try to console yourself daily after you have been shocked or alarmed by something. Simply get out of the situation and console yourself. That might take some courage and a lot of practice. Set the intention daily in the morning for these two things: “I have the help I need such that I can accept it in” and “I get taught by the right teacher for the thing I need to know”. You might get intrusive thoughts if you do this. If that’s the case, step out of the situation and consider what caused the alarming state. If it’s these two statements, let them go and console yourself. If you can console yourself just for 0.1% it’s fine. It’s enough. And it’s fine if it doesn’t feel as enough. You will survive and help is on its way. Sometimes help comes later than hoped. Maybe try to console yourself when things seem endless. You are stronger than this, I’m sure.
PS: stepping out of the situation, whether it’s in your head or with someone else, might require you to go to another room or take a walk outside. Anything that takes care of a soft reset.