Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
One-sided weakness of the body is most commonly due to a problem in the brain (as opposed to other areas of the central nervous system such as the spinal cord or peripheral nerves). Many possibilities exist, and depend somewhat on your age, your risk factors, and the nature of your symptoms (whether or not the numbness started suddenly or gradually, whether it is a complete loss of sensation or a tingling, whether it is an objective finding on examination or it is only a feeling that you have etc) .
The most concerning cause of weakness on one side of the body is a stroke. Please understand I am not trying to imply you have a stroke, but only that this is one possibility. Strokes occur predominantly in people with risk factors: smokers, high cholesterol, diabetics, hypertensives, and people over the age of 55. However, they can occur in any age. If your weakness was due to a stroke, it would start somewhat suddenly (over minutes) and would likely persist without significant improvement (which does not seem to be the case with you).
Other potential causes include multiple sclerosis, a brain tumor, a vascular malformation and others. Transient one-sided body weakness/numbness (lasting for example for minutes up to 30 minutes then resolving) could be due to a migraine (the aura of migraine, in which case following the numbness, a headache occurs) or seizures. Also, given the history of fibromyalgia, underlying pain/psychosocial may be the source of the symptoms.
You would benefit from evaluation by a neurologist. The MRI will be helpful to evaluate for many possibilities. Depending on the findings on examination and further history, additional workup may be needed such as blood work or spinal tap.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
I was diagnosed with fibromyalgia about 4 years ago. Since then I have also had increasing problems. The worst of which is currently vertigo, blurred vision, extreme light sensitivity and NO headaches.....lol. They always say do you have migraines. I have seen 4 neurologists. And they all say you have a problem but I don't know what it is and I can't help you! I also have left side weakness- arm, hand, face. I have had two MRIs.....no signs of MS. I hope that you get some answers because I can't. ANd don't let them tell you it psycological and it is all in your head......because it is not. Wish you lots of luck
Thank you for your response, My weakness has been gradual. I just realized I have been compensating with my left side. I do have what I call sparkle feeling in my hands and feet sometimes. I guess it could be described as tingling, but again I usually ignored it and thought nothing of it. I would just shake it out, or try to anyway. I am only 39 and at his point I am hoping for a benign answer to the symptoms. The weakness is also there at all times, and I never really have headaches except maybe once a month. It's usually hormonal changes that cause them.
Also,the hyperreflexia is in my left brachioradialis reflex but not the right.