I was perusing my dream / OOBE journal, and I think that I know the cause of the "presence" phenomena. It seems that, as far back as my notes go, the "presence" (and the associated physiological reactions) seems associated with my semi-regular OOBEs that occur in the early-dawn hours.... something that I don't pay a whole lot of attention to, and I document only when I have a clear memory of the event. My wife is used to all this; the dog, on the other hand, isn't.
I'm not sure if "something" or "someone" comes to get me during those times, or if this is simply an energy manifestation associated with the phenomenon. Since this is something that's been going on in my life for many years, I don't consider it remarkable. My very protective dog, on the other hand, seems to object to the whole business and tries to put a stop to it. I'll probably have to start putting the dog out at night--for the dog's psychological well-being, and so that I can get some sleep.
As far as I can remember, I've never visualized a presence or a being during these events--simply sensed it. Years ago, after reading Hopkins and Jacobs, I thought that all this was associated with "aliens," but I seriously doubt that "aliens" would bother to abduct me (or anyone else, for that matter).
Lest you think that any of this is bizarre or "woo-woo," keep in mind that this happens to most people at night. Most people travel out-of-body; few remember these events, and even fewer bother to record them.
I won't debate anyone who insists that there's no such thing as an OOBE. Personal experience is really the only thing that will convince the skeptic. Medical science at present denies that OOBEs are possible--they are explained away as "sleep paralysis" or, lately, as electromagnetic manipulation of the frontal cortex, which causes the sensation of being dis-embodied. So, until science catches up with the mystics, I'll continue to believe that what's happening to me is an OOBE.
While going through my notes, however, I found an interesting OOBE that I had many years ago. During the experience, I decided to see if it was possible to "possess" someone--in this case, my wife. I tried to dive into her body, but I found myself blocked by some magnetic-type force emanating about three feet away from her physical body. After waking up, I asked her if she had sensed anything during this time (she was half-asleep with her eyes closed), and she remembered seeing a bright flash of light, and then a neon-type light spel,ling out my initials.
I've read tons of stuff that purport to describe spirit visitations. Some of the spirits are good; some are evil. Personally, though I think it's a bad idea to dabble in this sort of thing; whether the spirits are "real," or simply projections of the percipient, is irrelevant. Once the genie is out of the bottle, it's hard to get it back in, and everything that I've read is that once you conjure something like this up, all sorts of unpleasant things start to happen.