Epilepsy and Driving - Query

Julia21

Hello
My son has nocturnal (during his sleep) epilepsy.  He had a provisional licence but stopped learning to drive when diagnosed 2 years ago.  His condition is well-managed on medication and he's not had a seizure in his sleep for over a year.  He's never had one in the day.
He reapplied to the DVLA for his licence and a month or so ago his GP rang him to write a report for same - as the DVLA had contacted his Doctor directly.
Today, he's had a letter from the DVLA telling him he 'must not drive' and that he'd had a seizure within the last 12 months.
As this is not the case, he's emailed his Dr for a copy of the letter they sent to the DVLA and asking for a reassessment - so he can ask the DVLA to reconsider.
However, reading the 5 considerations under the DVLA 'special considerations for epilepsy' point 5. mentions 3 years.  I just want to check as I'm confused: as I don't understand why asleep seizures would require a 3-year ban but awake seizures only 1 year?
I may be misunderstanding as it's been a long day but grateful for any advice/ thoughts please.
Thanks very much in advance.