Do you believe that he lost consciousness? If not, he suffered a complex partial seizure (also called psychomotor seizure). If so, he suffered a generalized seizure (previously called gran mal).
Mark your calendar for this event and for just what you witnessed. Duke's vet will need all the information you can gather when deciding if Duke should be prescribed an anticonvulsive drug. Most of us will accept one mild (lasting less than 5 minutes, no thrashing about, no loss of consciousness) event monthly before prescribing such a drug. Should Duke suffer another event within 24 hours of this one clustering is diagnosed and that may presage status epilepticus - the state in which seizure activity doesn't abate unless I heavily sedate or anesthetize my patient. Duke would then need the attention of a vet at your earliest convenience.
Here’s a quick synopsis of the type of seizures I see:
Partial seizures (previously called petit mal): focal or asymmetric sensory or motor activity affecting any part of the body (e.g., facial twitching, chomping of the mouth); can be associated with autonomic signs (salivation, vomiting, defecation).
Simple partial seizures don’t alter consciousness. Complex partial seizures cause the same symptoms as simple partial seizures and also alter mentation (mental status) and/or cause behavioral abnormalities.
Generalized seizures (previously called grand mal) cause diffuse motor activity with loss of consciousness.
Seizures first arising between the ages of 1-5 years are usually considered idiopathic (unknown cause) epilepsy. Seizures arising after 6 years of age are often caused by brain tumor or, less commonly, adult onset epilepsy.
Please respond with further questions or concerns if you wish. I regret that my state board of veterinary examiners doesn't allow me to speak to customers by phone in this venue but other experts in this category may be able to assist you in this regard. Please let me know if you'd like another expert to do so and I'll opt out of this conversation. Please stay in the conversation if you wish.