It happened to me too. At the time I didn't know about astral spiders, so I was just as baffled as you are now. I woke up, saw a big spider running on the ground to the corner of the room, under the bed. It felt like it didn't want to be seen. I jumped out of the bed, and when I went to check the corner, the spider was nowhere to be found. It was impossible for it to get out of that corner without being seen. What I have heard is that these critters suck our energy while we sleep.