Question: You are flying when you notice that your fingers and toes are becoming numb. You attribute it to the cold and turn up the cabin heat. The numbness progresses from your fingers and toes to your hands and feet, and you are having trouble manipulating the controls. You land at the next airport on your route and go to the hospital. The hospital runs a complete battery of tests. By this time you are feeling much better. The doctor tells you all of the tests were negative and they can't find a thing wrong. You leave for the airport to finish your trip. Are you legal?
Answer: Maybe not. FAR 67.309 states in part that neurologic standards for a third class airman medical certificate include "No established medical history or clinical diagnosis of ... A transient loss of control of nervous system function(s) without satisfactory medical explanation of the cause." FAR 61.53 also requires pilots to self-ground when a known medical condition makes the person unable to meet the requirements for the medical certificate held. In this situation, the FAA would expect the pilot to see the family physician, and maybe a specialist, to get to the bottom of the symptoms. If the doctor confirms that it isn't serious, you could continue to "self-assess" under 61.53 and resume flying on your current medical. Just be aware, though, that you should report the condition on your next FAA medical application, and be sure to provide your aviation medical examiner with a report from your treating doctor about the results of the evaluation.