I often get cramps when I don't think I have exerted myself too much, so I sometimes take the muscle spasms for granted. However, I have learned that muscle cramps are often the body's way of saying you are low on liquids.
Long story short, I was playing in a tennis tournament and began to cramp. I started drinking water immediately, but the cramps got worse as I sweated more. It was a hot day and even more so on the hard-surface tennis courts.
Anyway, I was sweating and sweating. Then at some point I noticed I wasn't sweating anymore, and about that time my entire body cramped. Seriously, I had cramps in virtually every muscle in my body. I ended up lying flat on the courts, unable to get up or move without pain. So my tournament concluded with a ride in a rescue vehicle to the local emergency room.
After the first IV I felt much better. I was told at the hospital that there are many dehydration causes, including sweating profusely during a tennis tournament.