What's going on with me?

I visited my doctor for anxiety many months ago, and he prescribed sertraline an antidepressant. I had a massive seizure out of the blue (im 22), and my boyfriend phoned an ambulance for me, and I stopped breathing for several minutes. I came around with a horrible headache, memory loss, and confusion (with some vomiting) and went to the hospital. My doctor changed the medication to valium and sent me away. Last night I was in the middle of central London and it happened again in a large train station. I only managed to piece this together after talking to people. I was in the ambulance that someone must have phoned for me, and I went back to the hospital, put on a drip, blood tests etc. I have had a CT scan - normal - and an ECG which showed that I had a high heart rate (normal with anxiety). Could the medications be causing this? I was not taking valium at the time of the first seizure, and not taking sertraline at the time of the second seizure so I'm not sure. I just felt so terrible and afraid afterwards and I am very worried about what the possibilities are. My seizures tend to be very aggressive and always a loss of consciousness, but dont seem to be more than every few weeks. Can you suggest what I need to do next, an EEG? I am very frightened.