Hey mate. I agree with Chops on this. Sounds like more of a step forward than a setback. You are an alcoholic so it's only natural that the odd sneaky thought will crop up. The secret is realising that it's just your addict mind. Give the thought no power and let it pass!! Which is what it sounds like you did. Then you can look at why you think this particular thought cropped up and work on anything that needs to be 'tweaked' in your recovery.
Posting about your experiences honestly as you do is a real positive. Plus when you get through these thoughts you gain strength and clarity. I always used these sneaky thoughts from nowhere to further ground my acceptance of being an alcoholic. If you think about it only an alcoholic would be struck down by this sudden maddening thought. The thoughts die down over time and grow less powerfull as you work your recovery and gain in strength, clarity and length of sobriety.
You're doing well mate. Peace