You can adapt the basic message when you want to tell someone casually about your epilepsy, and in a way that strengthens your relationship with the person you are telling. When opportunities arise during casual conversation, just be upfront about it and say you have epilepsy. Follow this with reassuring words giving some information about how your epilepsy affects your life. Depending on the person's level of interest, you can provide more information. You can end with giving practical information about what they can do to help if you have a seizure. If you think the person is uncomfortable with the information and worried about handling it, you can give them a contact number for them to call in the event of a seizure.
Well I suppose basically that you'd just explain that, number one that you have epilepsy. Explain that it's not the end of the world but that it has certain restrictions and that you don't know when you're going to have the seizure. But other than that your ability to function is reasonably okay but you're not as alert as you would be because of the medication I suppose and also that you probably do have mood swings and that type of thing.
I have a housemate. Now I just told him, by the way I've epilepsy, explained to him briefly and just gave him a phone number and said listen, just if I do take one, I said number one, just don't panic and just let it happen. And I said if he does tend to panic there's just a number to ring, I said that's my mother's and I gave my brother's number as well.