Symptoms of Altitude Sickness in Canines
The symptoms of altitude sickness are mainly due to the fact that the dog gets dehydrated and is unable to breathe normally. The symptoms of altitude sickness in dogs may include:

Panting
Excessive drooling
Vomiting
Pale gums
Bleeding from the nose and retina (only in extreme cases)
Increased pulse
Dry cough
Swelling of feet and possibly the face
Sudden collapse
Dizziness
Fever
Lack of coordination
Lethargy and refusal to move
The symptoms may vary and may be less severe, depending on how sensitive the dog is. If the ascent has been gradual, the dog may have fewer symptoms.

Detecting Altitude Sickness
Altitude sickness can only be detected judging by the dog's symptoms. If the dog displays this behavior whenever exposed to high altitudes and has no other health issues, the diagnosis may be altitude sickness.