Body off balance temporarily

Yesterday I ran my first 1/2 marathon. About 1/2 through the race I noticed I was feeling weak and my left side of my body was leaning towards the left. No matter how hard I tried I couldn't run upright and could not run at more than a slow jog.  I drank plenty of fluids during the race and have I have ran this distance in the past without any issues.  
Some background concerning my health: about 9 years ago I suddenly began having joint pain, nerve pain and neuropathy in my feet, fatigue, sudden weight loss and low fever. Doctors needn't know for sure what was wrong but began treating me for lupus.  
2 years ago I decided to try going gluten free to see if it would make a difference.  Well without 2 weeks I had no more joint pain and the nerve pain had decreased.  The neuropathy improved slowly.  Testing for celiac all came back normal but it wasn't done until after I had been gluten free for over 6 months. I did test positive for the genetic test for celiac.  
I am still gluten free but have been exposed to gluten several times over the last few weeks and have been feeling nausea often.  Because of this I haven't been eating well and have lost some weight (unneeded).
After the race I couldn't walk straight and I continued to walk leaning to the side. I drank gatorade and ate a banana and peanut butter. Slowly it improved.
Any idea what could have caused this.  I'm nervous about running now. Thank you.
Deb

[Christopher R Newey, DO]

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.

I cannot give you a definite answer without additional information, but typically one-sided symptoms (i.e,. in your case drifting to the left with walking) 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 one sided symptoms 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 symptoms were due to a stroke, it would start somewhat suddenly (over minutes) and would likely persist without significant improvement.

Other potential causes include migraine, seizures, etc.

You would benefit from evaluation by a neurologist. I would recommend that an MRI of the brain is performed along with vessel imaging. You may also benefit from an echocardiogram of the heart to ensure structural integrity. You would probably need to be evaluated by a neurologist before engaging in additional strenuous exercise.  

Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.