Jona26, I have to admit I know nothing about the support available to epilepsy sufferers, so I apologise in advance if this is useless, but…
I've done a few minutes' worth of digging and possibly found something. The railcard site says this on the eligibility page:
Please send in one of the following with your application
A copy of your Exemption Certification for epilepsy medication and a photocopy of your letter from the DVLA telling you that you are unable to drive
It then goes in to further detail in the railcard FAQ pages:
How do I find out if my epilepsy medication will make me eligible for a Disabled Persons Railcard?
We accept medications that are in line with Epilepsy Society guidelines. These are listed on the Epilepsy Society’s website. Because many of these medications have other uses, if you are applying on the grounds of your epilepsy you will also need to send in a copy of the Exemption Certificate that enables you to receive your medication free of charge. More information on the form FP92A, available from GP surgeries, can be found here.
Note that some of that paragraph doesn't apply to you, because the fact that the DVLA have said you can't drive means you
don't need to provide ATOC with a copy of your medication prescription. The pertinent bit for you is what it says about the exemption certificate. So, I had a look at the Epilepsy Society's website to which there were links in the above paragraph. Now, that says:
Free prescriptions
People with epilepsy are entitled to free prescriptions for their anti-epileptic medication, as well as any other prescribed drugs (but not dental treatment or eye tests). To apply for free prescriptions in England, fill in the form FP92A, available from your doctors’ surgery. In Scotland, Wales and Northern Ireland all prescriptions are free.
The underlining above is my own: it looks like as an epilepsy sufferer, you should be getting
all of your prescriptions free; even just, say, some antibiotics for something routine and not epilepsy-related. The way you get those free prescriptions is by filling in the form FP92A, and more information about that is on the NHS Business Services Authority website, which states:
How to apply
If you suffer from one of the specified conditions ask for an application form FP92A, available from your doctor's surgery. You need to fill in parts 1 and 2 and your doctor (or an authorised member of the practice staff) will sign to confirm the information you've given is correct.
[…]
Where your GP has confirmed that you have one of the specified conditions, we will send you a certificate. Certificates are valid for five years, starting one month before the date on which the application is received.
So, you see, there doesn't seem to be anything that says you need to be on epilepsy medication to get the exemption certificate – just that you need to have been diagnosed with epilepsy by your GP, as the certificate can be used towards non-epilepsy medication too. Therefore,
if I've interpreted everything correctly, you should be able to get the exemption certificate, which will in turn make you eligible for the railcard.
Good luck!