I would be wondering if there were a medical problem underlying this .... does he have other symptoms? GI problems, chronic sinus issues, migraines? Could he have an undiagnosed medical problem, such as celiac disease (http://www.celiaccentral.org/mental-health/Anxiety/614/) or low thyroid or testosterone (http://www.psychologytoday.com/blog/the-best-strategies-managing-adult-adhd/201304/the-great-masqueraders-depression-anxiety-low-en)? Is he on any medications that might have anxiety/depression as a side effect? If he's open to diagnostics, I would recommend doing a VERY thorough history and workup, preferably with a doctor who is trained in this sort of thing. It might take some looking to find the right professional.