I'm very sorry you are going through a tough time, but you are actually quite fortunate to have received these diagnoses. Many people with conditions like POTS just continue to go undiagnosed because it takes a keen, informed physician to spot them. It is important that you do see a doctor who specializes in dysautonomia not only for treatment, but also because often there is some underlying illness/disorder that is causing it. You may want to look into neurologists who specialize in this area unless the cardiologist you see seems thorough.
I don't know what your employers are like, but perhaps it would be best to keep them informed of your doctor visits, educate them on your diagnoses, etc.? Maybe if they understand what you are suffering from, they will have empathy and try to be lenient somehow? By the same token, you also must be lenient with yourself -- It is far too easy for people in our situations to be hard on ourselves, blame ourselves, try to push ourselves beyond our limits, and tell ourselves we should somehow be in control of our symptoms, or that they are "all in the mind", as some loved ones around us insist. Advocate for yourself, and let people (e.g., your wife) know that this type of thinking is not okay.
Best of luck to you!