What you describe also sounds like normal memory to me... simply thinking about the event. A flashback is typically a very short burst of memory, like what you describe, except it is triggered by something similar to what happened during the event itself. For example, you don't just lay in bed and suddenly start having flashbacks... you have memories, which include all five senses that get recorded into memory. That is how we associate smell. You know what a sausage smells like, so if you think about it, you can actually even remember the smell... as an example.
It could be a little of both... sudden memory combined with flashbacks. Don't really know for sure.
What I want to know is, do they ever go away?
Yes... they go away as you heal your trauma.
Will they be like how my nightmares were and just eventually lessen and leave and only come back when I am stressed out or anxious?
Flashbacks are very very rare... they are not something that typically hangs around... they are like short bursts of the past that usually occur during moments of being startled by something. When something hangs around, and you begin to lose memory of time and space or such, that is more into the dissociation areas.
Its very difficult to pinpoint what you experience, unless watching you within it. End of the day though... regardless what is happening to you, whether one or more of the above aspects, they are just symptoms, and symptoms go away / severely lessen as you heal the trauma itself.
I am more interested in why suddenly from a month ago! What happened in your life that put you under stress to begin having flashbacks or becoming distressed suddenly?