Could this constitute cheating?

I have just recently taken an exam and it has only now hit me that this might not be looked favorably upon by the professors.

A friend and I took an exam where the questions were predominately based on essays. The exam was an unseen exam, monitored and closed book. Together we spent many weeks working together in a group and prepared our idea of a perfect answer to questions that might appear. We made quite a few of these and memorised them all word for word. We studied by reading all the material together, talking about it and picking the key points and compelling quotes.

In the exam, we sat nowhere near eachother. We had no idea what questions might come up. I felt extremely good after the exam. I never thought I could remember the answers comprehensively that I prepared for my exam. We used mnemonics, a couple the same and some different to recall the plans for our essays.

The exam went incredibly well, the questions were perfect. All our hard work paid off!

Now, a few days later, I am wondering if this was a bad idea. Our answers will be remarkably similar, even though we both recalled it from our own memories. We haven’t plagiarised any sources, but have we plagiarised eachother?

I feel absolutely devastated. Have I some how cheated by accident? Here I thought I was doing optimum preparation. Now I am not totally sure. There are no rules preventing students from working in study groups. I’m not sure if this would constitute collusion, and obviously I can’t ask anyone now. I suppose during the pressure of the studying season it never occurred to me that we would learn it so well that we would both be writing nearly the same answers. I am sure we have some differences, but a lot of the sentences will be the same. Our conclusions are entirely different, and I added in a bit of extra things which I remembered on the fly, my friend did this as well.

I cannot find any rules against our method, in my university’s guidelines and no one else’s for that matter. I feel like I might have unknowingly thrown away my degree. This would totally devastate me, and worst of all it was unintentional. We both just wanted to learn the material as best we could.

Am I worrying unnecessarily? Have I become neurotic? My friend isn’t worried, my parents are wondering why I am so upset, no one I’ve talked to seems to think I should worry, but I can’t help it. This is such a horrible feeling.

I anyone could offer some sort of perspective, I would be so grateful. I know there isn’t really anything I can do about this, but have I even done anything wrong?