How do I know if I'm experiencing a delusion?
The first thing to know is that recognizing a delusion does not come easily- especially if you are not experienced in dealing with them. most people will only figure out that a belief is a delusion after the delusion has passed.
Here are some questions you can ask yourself:
Do trusted people in my life insist that one (or several) of my beliefs are not true?
Do I have a hard time backing up my beliefs with evidence? (particularly evidence that other people can agree with)
Are my beliefs consistent with my previous experiences? (e.g if you think your friend is trying to harm you, has that friend ever tried to harm you in the past or expressed that they want to harm you? is this a sudden change in character for them?)
Do I know what led to me believing this? (if this belief is new, do you know why you changed your mind?)
Do I have a hard time listening to other people's perspectives on my belief because my belief feels so obviously true?
Do I feel like other people are trying to lie to me or manipulate me when they offer alternatives to my belief?
No answer to these questions can single handedly rule in or out a delusion. They are just questions to ask yourself if you are questioning your belief.