Lost licence because of seizure, when will I get it back?

That's really difficult to tell and it's upto the DVLA to make that decision. If they think that you're unfit to drive (which they do and that's why they've revoked your licence in the first place), then you will have to wait until your circumstances change. They will normally contact your GP to assess your medical history and if your GP reports progress and thinks you are not fit to drive, then the DVLA will return your licence. To be honest, it all depends on your GP at this point. So you might want to go and see him/her to check when he/she thinks you'll be ready to drive again.