Having fear, butterflies, etc, especially on highway, is perfectly normal at the beginning, trust me. It happened to me. It last a few weeks or a month. But the more you expose yourself, the better you get.
Now, a bit of fear in a good way won't never go away. Or, I would say, paranoid behaviour, like expecting the worse from the cars surrounding you.
What is not normal I think, is if you ride and keep thinking about the accident. I just had my 1st major accident a few days ago, so I don't know how I will feel if I ride again. But my wife had a major car accident years ago, a truck also kill her and she had to visit a psychologist for that, panic attacks.
Just relax. Do not force yourself. If you do not feel comfortable riding, stay at home or practice on non busy streets. From there, take highways during off peak hours. You'll get better.
