Hey you know what, you might have a mental illness.
Don't worry, mental illnesses aren't that bad, it just means that your ill in a non-physical way - i.e. something to do with your head. Like anything else, they aren't always very severe. They are usually what they call 'spectrum' disorders - having severe and very mild extremes.
I have one myself. Its called OCD, and basically it means you fear something irrational, you have an anxiety, and you do a lot of things to try and relieve that anxiety. You might have nothing to do with this but I think its definitely a good idea to check this out.
You talk about intrusive thoughts don't you? Thats a sign of OCD, irrational thoughts that you can't control. Perhaps you 'fantasize' about suicide, even though there's nothing in the real world that would suggest anything like it, and fear your going to do it because your thinking about it? Perhaps you do things like put away knives or whatever to try to alleviate that anxiety?
So you should check it out. Its nothing to stress about, mental illnesses can be treated just like a common cold can be. See a GP, and don't procrastinate. If your thinking that what I'm talking about is way out of the world and completely impossible, well think again. Most people with OCD or other mental illnesses simply cannot realize anything is wrong, and everything just seems rational to them. You may think whatever but you have to consider the possibility that your just a frog stuck in a well. Reply to me and tell me what you think.
Good luck!