The single best question
Answer it in your head first, then look.
If you had to sort these two apart with one question, what would you ask?
When you get a satisfying answer, how long does the satisfaction last. For a question it lasts, because the question was answered and there is nothing left running. For an anxiety symptom it lasts roughly an hour, because relief was what was actually being sought and relief is not a lasting substance. Nothing about the content of the doubt tells you which one you have. The duration of the satisfaction does.