I don’t mean to sound insensitive, but technically you were doing things with demons. As far as most every religious text I’ve studied tells me, Satan is a demon. That being said, Satanism, to me, is an inherently dark religion.
Don’t get me wrong here, I have nothing against Satanists. I’ve been privy to a black mass or two, and even being a dabbler seems to draw negative energy. For a real Satanist, that negative energy is exactly what they thrive on, for someone dabbling though, it can be horrifying.
When you open yourself up to that kind of energy but you’ve not given yourself over to it completely you are inviting all sorts of bad things. I like to use the analogy of a Light House. When you are dabbling with dark forces you are in essence, a Light House in a fog of the unknown, and there are things that mean to have you in that fog.
I’m relatively young in physical years, but I have a very old soul, I’ve been around for a long time. That makes me both desirable to the dark things, and also very dangerous to them. The only reason I mention this is that you could be one of two kinds of people, an old soul that has been around for a while, or one of those sparkly new ones.
Demons and all manner of dark creature love the sparkly new souls because while they are inherently innocent, free of the stains from past lives, they are also easily seduced. They are easily taken and bent. This sounds a lot like at the time you were acting as that light house, shining in the dark, and something came to investigate.
I would recommend, just to be on the safe side, casting a Circle around you before any long term meditation. The wonderful thing about even the most basic of circles is that it will block out ALL outside forces. Leaving you to your meditation without fear of some curious being poking around at you.
If something like this happens again, and you had a Circle in place, let me know.