Absolutely real. So real that every human being will be depressed sometime in their life. It is just one of multiple mental states we have in our framework.
Nope. There's a difference between being sad and being clinically depressed, there's a difference between being distracted and having ADHD, there's a difference between worrying and having OCD, there's a difference between not wanting to eat a particular meal and having anorexia or ARFID.
Please. Having a mental disorder is stigmatized enough already. Please don't play into it by implying it's not real.