Sometimes I see a black mist as I am waking?

This has only happened like 3 times in the past year, but the first time it happened was when we were at our past house. It was anywhere from 9-11pm and I decided to go to bed. I began to fall asleep and then I had the urge to open my eyes and when I did I saw a black mist (almost tentacle like) coming towards me so I swung my blanket over it and it disappeared. I did a little prayer and grabbed a little cross and went to bed. I had a dream that the cross broke..but it was fine in the morning. Then last night the same thing happened (this is at our current house, don't think houses are or were haunted)...I felt I should open my eyes and I saw a little more cloudy like mist hovering right over my mountain dew can (almost like it was drinking some lol) I reached out to grab it and it was gone. I was kinda nervous for the rest of the night though. I just want to know what this could be or what problems could maybe cause this? Thanks a lot (p.s. im not crazy =] )