Wah, stumbled onto this thread, jolly great reading.
As freshie here, will start contribute one of my experiences.

Many, many years ago, biz trip to KL. Fedxxxxl Hotel, checked into old wing. Hotel was full, anyway, got into my room. Turned on the lights n left luggage on bed, as was about to unpack toiletries.

Just like in the movies, despite the lights on... I can actually see shadow n darkness engulfing the room, starting from far side of room towards me. (Wow, recalling n typing now, I still have goosebumps). The whole room suddenly felt cold n almost devoid of oxygen, causing a panic attack.

I just grabbed my barang-barang n ran out of the room. Went down to receptionist n wanted change room... The staff also never asked why, what's wrong. Like as if they dunno.

Told me old wing all full, if I want to change to new wing, self top up $$$ as above company rates. KNN, get scared n yet lose money... Still remember, never sleep that trip.