Well, I had some weird experiences during a period of a few months in the house I was at a the time, it felt like sometimes a very negative, energy sucking presence would come close to me, invisible to the sight but able of limited interaction with surroundings. Somehow my cat picked it up exactly at the same time as me and look and hiss at the same point as me, and then jump forward and fight it, even though it was clawing furiously at the air to me. His attacks would terminate the presence quickly. He never attacked when I would not feel the presence, he was never one of those quirky felines.
The presence would manifest with a sense of anxiety and cold chillls on my skin, as well as a cold breeze.
This cold breeze thing was particularly upsetting as it happened also on non windy days, and I had seals on all doors and windows, and nothing was open.
Then after a while the presence became stronger and would impose more of this bad feeling on me and manifest more frequently, as well as started to move things.
You could say that it was my cat but I had many episodes where my cat was in my sight when something fell, or that he came to inspect the source of noise from another room.
What convinced me that I was not making up things was when I had just been in a room that had shelves with books, then left it and closed the door.
Few minutes, I get the cold chill feeling, the cat gets in front of my room, looking down the corridor that leads to the closed room where I sensed the presence.
I get up and get close to my cat, then a thump sound comes from the inside the room, I go and open the door following the cat that is rushing the door, I open it and my cat attacks something invisible howling in fury.
A few seconds and the presence dissipates and cat calms down immediately.
The source of the thump.... well the bible was on the ground instead of being on the shelf (I am not religious).
Anyway, I spoke about it to a witch friend of mine, and she came over and identified the presence as a lower tier demon, not really even conscious or self aware, just intent on provoking feelings of fear to feed on them.
Quick basic ritual was performed and the presence was never felt again.