If you observe your cat having what you believe is a seizure, the most important thing to do is to observe every detail you can about it so it can be described to your vet. Frequently, your vet will never actually be able to observe your cat having a seizure, so your description is important to the diagnosis. It is important to observe which parts of the body are involved. After the seizure is over, your presence and attention will probably comfort your cat as it regains consciousness. Please note that there is an incredibly wide range of symptoms associated with seizures.
Generalized convulsions are rare in cats.
If a cat is having a single prolonged seizure, continuous seizures without recovery between them, or two or more isolated seizures within 24 hours, seek medical attention immediately. Aggressive treatment is recommended, usually intravenous dosage of diazepam. Your close observation and careful description will help your vet make a diagnosis. A complete physical and neurological examination should be performed on any cat with seizures. Often blood tests are indicated to detect any generalized illness that may be causing the seizures.