Re: [Private]
It's the fact that so many are bringing them up at the same time that interests me. There are such things as mutual delusions and mass hysteria. This has some of those hallmarks. Things that before went unnoticed are suddenly interpreted as reasons to be concerned, simply because another person shared a similar, usually frightening, experience.
There is one other factor, though--something that's more difficult to explain. These dreams seem to take place in very unfamiliar settings, sometimes unfamiliar time periods; but the dreamer, in the midst of the dream, feels that they understand the backstory, and it makes sense to them that they are in these exotic locales. That's something I experienced myself in the case of my strange dream. I was on an Island, and was able to walk around this Island like I'd lived there all my life.
Again, with a single case, that element would probably go unnoticed. But when were are so many... well, it's a little odd.