Less serious side effects include: 1  Loss of appetite. 2  Weight loss. 3  Nausea. 4  Vomiting. 5  Diarrhea. 6  Frequent urination. 7  Muscle cramps, painful and swollen joints. 8  Excessive tiredness. 9  Difficulty falling asleep. 10  Headache, nervousness, dizziness. 11  Depression, mood swings. 12  Vivid dreams.
Nausea can occur in dogs for many reasons, particularly when the digestive tract and nervous systems are out of balance. Stress can certainly play a role in nausea.
1 A common sign of your dog developing stomach ulcers is blood-tinged vomiting. 2  Aspirin should not be given to puppies and cats as they lack the necessary enzymes to breakdown the aspirin which can result in severe organ damage.  Aspirin is also not recommended for dogs that are pregnant as it may cause birth defects.