Oh great. There was a big spider in my room, so I went to get something to scoop him up with (or flatten, I hadn't decided between the two yet). I come back and he's disappeared. 
oh oh, so now you don't know where your enemy is hiding.  Sounds scary.
It's scary and annoying because now I have to systematically check every inch of my room because I'm definitely not sleeping here with that big ol spider somewhere in my room!
How annoying, but would be wise imagine it jumping on you while you sleep.