Most of the things I felt I could have done differently pass through my mind in high default mode network states. The thoughts come on rare occasion and sporadically, usually in the form of visions of actions. The visions are not accompanied by emotions—my attitude is along the lines of "what is done is done; learn (or don't), and move on."
That is not to say I do not experience regret. I would say I feel it far less than most others based on experience, and that the feeling itself fades quickly. During the feeling(?), I am self-critical, but not harsh. We are all prone to make mistakes. Those who have spoken to me at length know that I am quick to forgive or simply disregard most actions of others against me.
I don't often think about my past. The past has always seemed like a blur, and it was like that long before I ever had my first sip of alcohol. With context or concentration, I can bring up vivid memories. My semantic memory is good, but my autobiographical memory seems disjointed.
In a sort of parallel, the future seems nebulous to me. This is something I have been working on.