Hi Sandra @sksnow, welcome to Mayo Connect. Finding lung nodules or masses is always concerning, rightfully so. It's also easy to let your mind run to the worst scenarios. I'm glad that you've had the bronchoscopy, which will determine what the mass consists of. Try to focus on what you know now; that something suspicious was found, and that you should know more soon once the biopsy is resulted. Most nodules are non-cancerous. Expect some coughing for a few days after the bronchoscopy, as the tissues will be irritated.
I admit, I had to look up "SIADH" (https://www.mayoclinic.org/diseases-conditions/hyponatremia/symptoms-causes/syc-20373711). I'm sure it's hard to know if you don't feel well due to the SIADH or if it's an additional issue.
How large was the mass/nodule that they saw on the CT? How are you feeling after the bronchoscopy?