I felt the same at Lydford castle. It's a very small town, one street with only a few houses, so there was no one around and we wandered about sort of soaking it all in. I could imagine what it might have been like a thousand years earlier, and it was interesting to think about the liv s that lived in those times as you have said.
Not too far down from the castle is a little waterfall which I'm sure would have attracted people then as it does now. We sat and imagined we were there a thousand years ago. A nice moment.
I wonder if there was any furniture inside the castle. Around here, in some castles one can get an idea of how difficult that life was by the size of the furniture, the beds are very small. The people of that time were probably so small because of malnutrition, including the nobility.
Most of the ones I went to in England were fully furnished (except for those that were ruins). Lydford was ruins; intact outside but inside basically nothing. It's an empty shell, just the masonry, no timber flooring etc. It gave off a spooky vibe, maybe some of the events of the past had permeated the walls?
I imagined that only the shell remained... it's a pity. About the energy. Maybe it is autosuggestion, but in some places I have also felt that, as if an energy had been impregnated. The point is that I do believe it is possible to have this kind of experience.