You would not necessarily have to be confessing this to anyone else than a therapist if you chose one to work with.
Is your anxiety level higher than usual? The compulsive thinking may relate to OCD.
These thoughts are causing you significant distress. You don't have to send the thoughts to the past. You're working with the present moment and the current thinking pattern that is taking control over your health.
Thoughts are self generated. Thoughts can be modified by paraphrasing them, redirecting them to a neutral or positive object of attention and through practicing mindfulness. For example, on any given day, you may decide to put aside some worry time for let's say 5 minutes. During this time, you can allow yourself to bring to mind all sorts of thoughts regarding this incident. At the end of the 5 min marker, notice how many different thoughts had arisen to your mind.
The next day, reduce the time to 4 min, then 3 min, etc.
Meditation can be effective in reducing anxiety as well as enabling you to bring your awareness and view the thoughts as thoughts rather than realities. Then, you can try to reframe these sorts of negative/anxiety provoking thoughts.
If the self help tools you've used are not as helpful, working w/ someone face to face who specializes in Cognitive Therapy or CBT (cognitive behavioral therapy) may be helpful. Another thing to look into is what is your general level of anxiety. In some cases medication helps balance the brain chemistry as a result of one's thoughts can become more manageable.
Jack, this would be something to do beyond online consult; it is causing your health to deteriorate. Logically you know that you're making this more of an issue than it is. Yet, the thoughts and anxiety are running your life now rather than the other way around. Any trained clinician can hear what you're dealing with without judgment or negative consequences.
The Imp of the Mind: Exploring the Silent Epidemic of Obsessive Bad Thoughts by Lee Baer
Overcoming Obsessive Thoughts: How to Gain Control of Your OCD by David A. Clark and Christine Purdon