Snakes and spiders seem to be relatively common entities to see, and they are usually not very nice. Many people have attacks/sleep terrrors when they are younger and snakes and spiders have to be up there as some of the most common forms to scare the hell out of people. I have a friend who sees large spiders (size of fist) crawling around sometimes when he wakes up in the mornings, but to date he doesn't seem to have experienced any attacks. I have another friend who used to have night terrors in which snapes and spider would be crawling all around him, falling through the ceiling etc and obviously, he hated it.
Personally I have never seen a spider but had a snake bite me in a dream and I felt it in my upper leg - ouch!
The spider was possibly getting ready to feed off you while you slept. Maybe it noticed you could see it and so puffed itself up to look big like so many animals do when confronted.
Oh and for what its worth, I remember reading some channeling on UFO's on Spiritweb (thought it was "Mission of the One Star" but can't find anything in it now), and one of the ET civilisations was spider creatures. Reminded me of what you said. They were on the whole negative in nature, like huge spiders. If I remember correctly they destroyed their planet by playing too much with black hole technology, or something.
I know it is damn hard not to be scared when you see something like that - I would be rushing adrenelin too - but unless it hurts you....
Gold is a good colour too. Maybe it has been reformed?!