Hereditary epilepsy is not a common problem for the Cavalier Spaniel breed, though it does occasionally happen. If present, seizures can present themselves unexpectedly and most often in a dog between 6 and 12 months of age.
If affected, your Cavalier King Charles Spaniel can generally be successfully treated by drug therapy.
A related condition is often called “fly catching behavior,” where a dog seems to be snapping at nonexistent flies. This condition is frequently left untreated as the dog is rarely harmed by this bizarre behavior.
Another unexplained behavior that appears to be similar to epilepsy and “fly catching” is sometimes referred to as episodic weakness.
This presents itself as a dog that suddenly stiffens, lowers its head, and may tremble or even fall over. Generally, the behavior subsides within a few minutes with no apparent harm to the animal. The cause of this behavior is not yet known, and there is no recommended course of treatment.