"Possible dehydration" means that there is a chance or likelihood that a person's body is lacking sufficient water, which can lead to various health issues. Full definition
Individuals having difficulty breathing, shortness of breath, or are dizzy and weak from possible dehydration, should seek medical evaluation immediately. (www2.erie.gov)
Mouth breathing also accelerates water loss increasing possible dehydration. (breathing.com)
If the response isn't normal, it's a sign of possible dehydration: (laurelwoodvets.com)