Just finished reading the whole thread over the past few days, which I found fascinating and, at times, very creepy.
One trend that strikes me about the experiences described is that many of them occured when the person or people involved are likely to be in an understandably heightened state of anxiousness, such as having recently suffered a bereavement or having just moved into a new home etc. These situations are out of the ordinary and stressful, and this is on top of the usual stresses of modern life.
Humans have evolved for over 1 million years to survive dangerous situations and physical threats, but modern life is usually so ordered and mundane. You can't just switch off those instincts, they come out in different ways. When something stressful happens, I think that the mind searches for a threat, and if it doesn't categorically identify something definite, the mind makes something up to fill in the blanks.
There's so many reports, many of them with similarities. I don't doubt that people have seen something, but I don't think that what they've seen is real. It's just in their mind.
I'm 46 and have led a very active life, full of highs and lows. I've experienced coincidences but have never experienced anything which borders on being supernatural.
They don't exist, but please do keep posting stories!!!