What are focal seizures?

23f 115 5'7.

Went to the emergency department the other day. I had a really, really, really strange metallic and burning taste in my mouth and I had the world's most like rising feeling in my stomach, vomiting, and horrible sense of doom, shakiness and feeling confused. My heart rate was up. After this subsided I just felt really weird and tired and out of body. I was at work when this happened and my manager sent me to the ER. Upon arrival to the ER the nurse immediately asked me if I've had a seizure before.

The ER doctor was a super nice guy and he did a full workup on me. Did a full cardiac work up and d-dimer. He also did a non-contrast CT. He said everything looked "fantastic" and that He does not see anything that is life-threatening going on. But then he mentioned focal seizures. I have never heard of these seizures before and it might be beneficial to speak to neurology as he cannot say for sure. What are these? Also, what are the chances that a CT w/o contrast can miss a mass? Because I've heard that seizures can be caused by a mass in the brain.