What is wrong with my friend? urgent please help!?

One of my very good friends has had epilepsy for almost his whole life. He is now middle aged, and before a few months ago he had his epilepsy controlled through medication. However, just about a month ago he had an "episode" while he was at work. All of the sudden, he lost the ability to speak. He could think, but could not express himself through speaking. He said he felt very strange. He was rushed to the hospital and drifted in and out of being able to speak for a few hours. All of the doctors he saw had no idea what was happening. He had a CAT scan and lots of other tests but they have found nothing abnormal. He has not had another episode until today. He was at work again when he noticed he couldn't speak. He drove home, took a bath, and then felt better and went back to work. I am very worried for my friend and was wondering of anyone had any idea what is happening to him. Thank you!