My cat has seizure-like episodes, then seems fine. Is it serious?

Sorry to hear that Sassy isn't acting right. If she seems to act completely fine after these episodes, it is highly unlikely that we are dealing with a seizure condition. Seizures are usually coupled with long periods of disorientation afterwards lasting hours to days. You may be seeing episodes similar to fainting or partial loss of consciousness. These episodes are typically associated with cardiovascular health such as a blood flow issue or a primary cardiac disease. Cats can throw clots resulting in a condition known as saddle thrombus. When this happens they tend to have very cold extremities, and also tend to be EXTREMELY painful. If Sassy does not appear to be in considerable distress and pain, this is not likely to be the case. I would definitely recommend having her examined as soon as possible to check for any sort of cardiac dysfunction. I would also make sure to have her blood drawn and to have a blood pressure checked. These will be important diagnostic tests to determine what may be happening. Hope this helps!