Yes I can relate. I woke up awhile back at 3:45 am (almost exactly) for nights on end. I am sorry this is happening to you. You say you reconize this as also a flashback..I don't know your specific circumstances or past trauma but I bet you are right. For me, when there is a consistency in what time I am jolted awake in the night it was my body actually reliving what happened to me as a child. It is scary and awful. Often my body and mind experienced great discomfort. I just try really hard to figure out my body is telling me and I often ask God "what is REALLY going on?". Depending on the night I either embrace the emotion and cry it out, or sometimes I get up and turn on all the lights in the house,sit infront of the tv and just try and feel safe again.
It really sucks doesn't it?
If you need help talking it through..shoot me back.
Hang in there.