What is Real and What is Not?

I am told that an ADHDer might overthink many things in his or her life. I often predict the worse and see very few options when stuck in a situation. To be told that it is just the ADHD thing is somehow a relief. But now, my bigger question is, what is real and what is not? Probably this is where I need someone to talk me back. To tell me and guide me that what I overthink is half true. Choose this one and forget the other. Concentrate on A and leave aside everything else. But I don’t always have that privilege. It’s a constant struggle and I don’t want it to destroy my ability to trust my own self.