Right so this sort of thing is exactly why I got into ghost hunting in the first place - that feeling of seeing something you can't explain and it just sits in your head for days.
Few questions before jumping to conclusions though. What time was it roughly? And was there any sound at all, even faint? That's usually the first thing I try to nail down when something weird happens. Drones are everywhere now and they can look pretty strange hovering against a dark tree line, but they've always got that annoying buzzing hum if you listen for it.
Also what part of the country are you in? Flight paths, military activity, all that stuff is worth ruling out first.
Not saying thats what it was, just saying the detail matters. Describe it as best you can - shape, colour, did it move at all or stay completely still? The more specific you are the more useful the discussion becomes. People on here are good at picking things apart once they've got something to work with.