I endured severe MC symptoms when I was at school but I got through it okay, I was lucky to have some good friends.
I have no reaction to sugar but as Jan says, one of the maddening things about Myotonia Congenita (MC) is that no two people seem to experience the same symptoms!
I had very enlarged muscles before I started on Mexitil, a drug that helped lessen the MC, unfortunately it is no longer available. I now take Flecainide but I have to have frequent reviews with a neurologist because it is a heart drug and although it allows my muscles to behave almost normally there is a risk involved in taking it.
There are a lot of very knowledgeable people using this forum so if you have any further questions post them here and someone will give you an answer.