Why are you blaming the supplement?

Your body probably has pathogens, parasites and other trash inside it. If you want to clean it up sometimes the body has a toxic reaction to the residue stirred up by beneficial supplements. I personally do not like to stir those things up and use Bentonite to slowly move the toxins, parasites and other trash out without the ill effects. If you want to cleanse the body use juicing,bentonite, and psyllium together. Start slowly until the body is able to do more until you can move to three doses per day of calcium Bentonite clay. You may become constipated at first as the body tries to move all the garbage out of the body. It takes time and when you get to two or three well formed healthy stools each day with no ill effects then you will be on your way to a healthy happy life.What you have is called a cleansing reaction.

http://www.rawfoodinfo.com/articles/art_cleansingreacJameth.html

You didn't say how much MSM you were taking. Perhaps your liver can't handle it right now. Or, maybe you filled up your body deficit. Whatever it is, it sounds like your body is saying Thanks, but that is enough.

Ronbn49 is right. Your detoxing and detoxing burns lots and lots of energy. I see people post all the time asking why they have this symptoms or that on detox supplements. MSM, NAC, Glutathione, Selenium, Zinc, Black Radish, Reishi, Capryl, probiotics, kefir, Vit C, coconut oil, B- Complex, Iodine, cilantor, kale, parsley, Boron, fresh fruits and veggies and a host of others can cause herx.

Do you still take MSM ? I noticed something similar but wasn't sure if MSM was causing it. I noticed a lot of energy and clarity of mind the first few days. But now whenever I take it I have extreme weakness and brain fog. As if my brain is struggling got oxygen.