I feel like I'm lying about my disorder

Like the title said, I have imposter syndrome over this disorder. I have the usual symptoms and I've been diagnosed twice, but still today I couldn't go to work and I feel like such a failure. I have these overwhelming thoughts saying I'm pretending, I do this all for attention or to miss work but when I try to act differently I can't. I don't know if imposter syndrom is compatible with a disorder, if I'm just really lying or if PMDD is just the AH it is, making me believe stuff about myself. Has anyone ever felt that way ?