“Silent seizure” is a phrase people use, but it is not a precise modern seizure type in the ILAE classification. It can mean different things depending on who is speaking.
Why I personally use the phrase
In my own case, EEG monitoring recorded four seizures during sleep that I did not know I was having. Looking back, there were small visible signs such as twitching. That is why I personally describe them as my “silent seizures”. It is my shorthand for seizures I was unaware of, not a formal medical classification.
It may mean a seizure with very little outward sign
Some focal seizures and absence seizures can be subtle. A person may stare, pause, stop responding, experience an internal sensation or have only a small movement that is easy to miss. To an observer, the seizure may look “silent” even though it has clinical symptoms.
It can also be used for electrographic-only seizures
In EEG terminology, an electrographic-only seizure is seizure activity recorded on EEG without an evident clinical sign at the time. ILAE neonatal terminology specifically prefers “electrographic-only” over older phrases such as “clinically silent” or “subclinical”, because absence of an observed sign does not prove that the event has no subjective effect.
A second seizure on EEG does not automatically tell you what it felt like
If monitoring records an electrographic seizure that nobody noticed, the recording can establish that an electrical seizure occurred. It cannot by itself prove exactly what the person experienced unless the clinical record, video and EEG are reviewed together.
Why precise language helps
Instead of “silent seizure”, it is usually more useful to describe what is known: a focal seizure with subtle signs, an absence seizure, an event noticed only retrospectively, or an electrographic-only seizure. That avoids making all invisible or unobserved seizures sound like one condition.
Sources
ILAE — Updated classification of epileptic seizures (2025)
ILAE — neonatal seizure terminology, including electrographic-only seizures