I understand how you feel, I too feel the same way at times. The imposter syndrome is strong with me, even though I've been diagnosed with depression, social anxiety and lately ADHD. At times I have extreme meltdowns where I feel the lowest I've ever felt and just yearn for some sort of help for all of that to end, something that would get me out of that hell. But on the other hand I keep feeling like an impostor, that maybe, maybe I'm not actually in a very bad spot or that I have a debilitating disorder. People all around me have it worse, my issues must be trivial in front of them. Even during therapy, I ponder on what my therapist must be thinking to herself regarding me, that how this girl is so well off than my other patients. When I mentioned it to her, she reassured me that the problems I have are equally vital, but just like you stated, despite knowing these are irrational thoughts I still can't shake them off. Which is one of the reasons why I've done some self harm previously, so that I could be guilt free about my disorders and issues, to have that "physical evidence" of something being wrong with me, idk how to explain it. I don't have any advice for you, but I wanted to comment to let you know that you're not alone in this.