Often times people with intrusive thoughts such as you describe have OCD - Obcessive Compulsive Disorder, which is accompanied by extreme anxiety. You should seek treatment with a psychiatrist who can make the diagnosis and offer the best treatment for you. I know this is scary to you, however it is a common disorder that responds well to a combination of medicine and therapy.
Only a professional can sort through whether or not these are just intrusive thoughts, which are harmless, yet scary thoughts that come with anxiety and panic...or if there is something more serious and intentional behind these thoughts.
You need to be seen by a doctor and have a thorough assessment. They'll be able to determine what exactly is going on.
Don't put it off...and obviously, if you aren't sure about your intentions, it would be wise to seek emergent help by going to your local ER.
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