Eades did a post about low carbing and cramps, loss of electrolytes etc. He used to get wicked cramps in his legs and hands. Turned out he was very dehydrated as drank lots of coffee and not much water:
The Blog of Michael R. Eades, M.D. » Tips & tricks for starting (or restarting) low-carb Pt II
Lots of good info for drinking water to remain hydrated.