For several years, I have had a recurring set of symptoms. These include a low-grade headache, nausea, some loss of coordination (especially observed in computer keyboard mistakes and what feels like difficulty pronouncing certain words), difficulty concentrating, and a general mental fog. The symptoms last approximately four weeks before fading, and they recur approximately every six months. During my last episode, my doctor ordered a variety of blood tests (e.g., Lyme disease, HIV, etc.) all of which were negative. Is there any neurological condition that is consistent with the episodic nature of my symptoms? Thanks.