[anonymous]

The gastrointestinal distress is a symptom of the neurological disorder, by treating the seizure disorder the gastrointestinal symptoms should be alleviated. Thereby eliminating the need for the other meds and additional testing, discuss with the vet.
See excerpt from Simple Partial and Complex Partial Seizures https://www.vetinfo.com/partial-seizures-dogs.html

Simple partial seizures are localized and originate in that area of the brain that controls movement. The face is the area that’s most commonly affected. Abnormal behavior, such as twitching or blinking is observed usually on one side of the face. Thus, this type of seizure is asymmetric in nature. The dog is alert, aware of his surroundings and confused by what’s happening. This seizure might spread and affect other parts of the body as well. In such cases, buckling and twitching of the limbs might be observed. Simple partial seizures may end or degenerate into a general seizure where the pet might lose consciousness. Complex partial seizures originate in that area of the brain that controls behavior and are also called psychomotor seizures. In such seizures, the dog’s mental awareness is hampered. During each such seizure, a certain form of abnormal behavior is repeated. Examples of abnormal behavior are lip smacking, hysterical running, aggression, biting, hiding or crouching and fly biting, when it appears as though the dog snaps at imaginary flies around his head. Such behavior is often accompanied by salivation, flank biting, vomiting, diarrhea and unusual thirst or appetite.