It sounds like you may need to discuss the results of neuropsychiatry testing and memory testing with the physicians who ordered them. It will be helpful for you to know the exact results of those tests, so that you can put that in perspective with the results of your other testing. Overall it sounds like you have had a very thorough workup for your deficit in short-term memory. It is encouraging to know that your MRI and EEG
were normal. You are correct that sleep apnea can cause memory difficulties for some people, but if you have been told that your sleep study excluded sleep apnea, then that is also an important negative test.
It might also be helpful for you to go back to your primary care physician
to get a big picture view of the results of your various specialist visit. In addition, it might also be helpful for you to discuss with a physician who knows you well the possibility of seeing a psychiatrist
as part of your work-up. Memory difficulties can be caused by many different things, and your statement that you see your memory loss as a "defense mechanism" against worrying suggests that it might be worth discussing your memory issues with a mental health specialist. Good luck.