Dehydration

Alot of people think that they're hydrated because they drink coffe and sugary drinks. Truth be told those liquids dont hydrate you properly. Most people find out that they're dehyrdated when they start exercising or the temperature starts to inrease. Here are some symptoms of dehydration

dry mouth,

the eyes stop making tears,

sweating may stop,

muscle cramps,

nausea and vomiting,

heart palpitations, and

lightheadedness (especially when standing).

The best things to rehydrate you are water and sport drinks. Reason for sport drinks is that they have electrolytes which your body needs. An electroltye imbalance can cause symptoons similar to dehydration
Check out these links for the symptoms of both conditions

http://www.medicinenet.com/dehydration/article.htm

http://www.buzzle.com/articles/electrolyte-imbalance-symptoms.html