Just as the wind which you can feel but not see, there are times when I've felt the presence of someone/something around which just wasn't visible (I see dead people...hahahah it ain't like that at all!!). Maybe this has happened to some here too. However, its all in your mind and I feel that the biggest influence is your upbringing...Coming from Nepal, Gods, demons, prophets are a talk of everyday life so there is no way we can completely deny its existence even there is no scientific proof for these phenomenons.