Huge very good changes are causing me to over-think. Some dark looping thoughts that are bothering me. Need some advice.

So I've always been a very relaxed, easy going person. I've always been a very positive thinking person and for the past 2 days I've had these looping thoughts I can't get out of my head and cause me to think and worry more.

Here's some back story. I was married to a very abusive wife about four years ago, it was very tramatic. I was only with her for 8 months because it was so bad, thankfully I managed to get out of it. I basically married her because I thought I finally found someone that actually loved me. So for about a year after that I drank and partied a lot and became depressed but I managed to pull myself out of it and become happy again, the binge drinking still existed but only on weekends. Further on, about 2 years later I lost my job and had to take a lower paying job which I still work at. I do like the job but it caused me to become in debt. I had a really expensive vehicle which I had such a hard time selling. So basically the past four years have been stressful but I've managed to maintain a happy and calm demeanor, always thinking positive. Rewind about 2 months ago, I finally sold my vehicle, have a job that I enjoy AND, this is the most amazing part, found the love of my life, having something as real as this has been the most amazing thing in my life. Things have really started turning around for me in a very real and positive way.

One night however, right before I fell asleep next to her, this thought came into my head that "What if I killed her" Not "I want to kill her" but What If? Like an accident or if my subconscious did something I didn't want to do. This irrational thought has been haunting me for a couple days now, I would NEVER EVER do anything to harm her but you can imagine what kind of torment this has been causing me. Now the thought is more of a blur than anything but its still causing me grief and I'm stressing about it. I've tried meditation, a logically rationalization of my current mind-state and what I think is that my subconscious is rejecting all of these good changes in my life after being in somewhat of a peril for such a long time. The change in my life is huge, I've given up smoking, finally enjoy my job, quit drinking/partying, now able to save money and get ahead and found the most amazing woman I have ever met. Is this my subconscious trying to hold onto my former life?

I found this quote that I found interesting: You are not your thoughts. You are the awareness behind the thoughts. Thoughts are often negative and painful, yearning for or fearing something in the future, complaining about something in the present or fearing a matter from the past. However, the thoughts are not you, although your ego wants you to think that. Awareness of your thoughts without being caught up in them is the first step to freedom.

Thanks