They shouldn't 'tell you off ' for it, though they might complain if you didn't tell them about it until you returned to work (difficult I know sometimes).
If they keep records, yes, it will go on your record.
It will go on record as sick because you was sick.
I cant see the company saying anything about the day off if it due to epilepsy as long as the company knows about your epilepsy.
If they do tell you off ie warnings they could be libel for disability discrimination but i doubt the company will say a thing.
Most companys now have a back to work meeting for when employees when they have days off work it just to ask if your ok and see if the company can help you.
You might also have to fill a form in to say you have been ill and not doing diy or been on holiday.
You can use a self sickness certificate for the first 7 days of any illness. A Dr will not issue with a certificate until after this period. Your employer cannot tell you off for taking one days sickness. It will go on your record.
I think you should read your contract of employment.