Mate that feeling of not being able to stop thinking about it is so familiar, it almost becomes a physical sensation doesn't it. Like something has shifted and you can't quite go back to how things felt before.
What colour was it roughly? And was it completely silent or did you get any sound at all - even something low or distant? I ask because I had something similar over the fields near Matlock about three years back, just this dark shape holding position above the tree line for what felt like a long time. No lights, no sound, just... there. Then gone. No gradual movement, no fade, just absent.
I've gone back and forth on what it was ever since. A few people I've spoken to locally had odd experiences around the same time which makes me think whatever it was wasn't unique to me.
Definitely post more details if you feel up to it. These threads are always worth documenting properly even if nothing ever gets fully explained.