What is on me?!

I had walked outside to put some more things into the recycle box. I had come back inside and seen something out of the corner of my eye. I glanced down to my shoulder and saw something kind of move a little. I FREAKED out and brushed at my shoulder over and over while jumping/running in little circles. This went on for a couple seconds even after whatever had been on me was off. B was sitting at the computer and asked what it was. I calmed down enough to tell him that I didn't know, but I was looking for it. It took me a minute to find it and when I did, I really freaked out! This monster of a spider had been on me! I know that it doesn't look big but it was probably about the size of my head. Ok obviously it wasn't that big, but when one such as myself sees it perched on one's shoulder, I think to myself, "Self! What is that Goliath thing on you!" After we used almost an entire can of spray(per my request) and after it had fought a good fight, it died. Whilst we(when I say we I mean B as I kneeled on a high, safe place some distance away) was spraying it, it tried to run away and with legs fully extended it was probably about the size of a nickel. It was awful awful awful! I feel all itchy and paranoid that another one is somewhere on my person. Yuck!