When you're getting dehydrated you should notice these early signs such as Dry mouth, headache, Dizziness, Low Volume of Urine that is more yellow than normal.
You might also feel sleepy or more tired, and dry mouth and notice an increase in thirst.
You should always drink something to stay hydrated before you feel thirsty to prevent dehydration from happening.
Severe dehydration can be life threatening and requires medical attention.
But most cases of dehydration can be resolved on your own by replacing the lost fluids before the dehydration gets too severe.