Epileptic seizure occurred after 21 years

My mum had a stroke back in February 2002 and following a discharge in May 2002, she started getting seizures around every 1 to 2 months and the doctors were trying different medications until one started working. The seizures stopped in around 2003/2004 however she was taking oxcarbazepine and has not stopped since then.

However last night she ended up getting a seizure after 21 years being seizure-free.

Does this mean they are going to occur more regularly following yesterday? Do they have remissions and relapse periods? The paramedics found it occuring after 21 years an unusually long period of time.

We will be seeing our regular specialist which she is still under the care of and going to have a scan.