Be careful with terms like “brain fog” because people have different ideas about what it actually is. I personally don’t connect memory issues with brain fog, but many people do. You and your doctor (or other patients) may be talking about something completely different. They likely will not realize that there is a miscommunication happening.
Perhaps the greatest source of miscommunication is what your doctor actually wants and how they see the world. A lot of them will mistreat patients where all of the tests come back negative. Some of them will even tell you that you don’t have POTS when the test comes back positive.
Some doctors simply don’t like dealing with patients if the patient’s medical condition is not something that they learned about in medical school. But they won’t come out and say that. Instead, they’ll tell you that you have “anxiety”, a “functional” or “psychogenic” disorder (your beliefs are causing your health issues), that you are “healthy”, or they may engage in some other form of gaslighting. It’s unethical for them to not treat sick people so one way of that is to conveniently misdiagnose you as a ‘healthy’ patient. For a deeper dive into that topic, see the Youtube video below:
On a practical level, you’ll want to gently probe your doctor whenever they don’t know what’s going on- even if some of your tests are abnormal. When they don’t know, they may decide to put crazy stuff into your medical records such as ‘anxiety’. And that can cause problems for you later. Do what you can to avoid dishonesty in your medical records and find a provider who will actually listen to the patient. You can ask your doctor if your symptoms are idiopathic (of unknown cause) and politely insist that your medical records reflect that.