I was doing an overnight at work - i'd been doing so for a week. I'd been sleeping fine, having no problems. In fact at the time I'd just gotten done posting a bit on AB and doing some case-studies. I went out into the main room at work and sat down to read a book - The Fountainhead at the time - and out of the corner of my eye I caught some movement. I looked up and at the corner of the main hall and the office there was this little smoky shape peeking around the wall. I didn't feel all that terrified - more along the lines of "huh". I didn't really have a response and just watched. After about 5 minutes, it slid around the corner and hovered there...apparently regarding me the same way I was regarding it. I set down my book, marked my page, and stared back for about another 10 minutes. It was persistently there. When I closed my eyes it was not still in my field of vision like an afterimage. When I shifted my head side to side it remained stationary in its spacial location. Finally, really intrigued but not at all nervous or frightened, I stood up and walked in an arc around it. It stood there, hazy and white - roughly the shape of a person. The craziest bit was as I walked around it, its shape was consistent with a person...actually a child (it was only about 4 feet tall). It was not like it spun to follow me - it had spacial context. It had less depth than width and height - it was entirely 3 dimensional. When I got closer, it didn't get further away (as I would expect if it were just a trick of light or an optical effect in my eye). Finally, I closed into about 1 foot of it and crouched down next to it so I was about head-to-head with it. It didn't move and appeared to be made entirely of smoke that was not moving - solidified. Like that aerogel stuff. I was mystified by it, especially because since coming around the corner it hadn't moved and almost seemed to be allowing me to inspect it. With this as my general feeling about the situation, I decided there would likely be no harm in testing it further. So I reached out my hand and it passed right through the thing like it was nothing - no change in temperature, no distortion of the constituent smoke - but then it just dissolved into the air and was gone.