Yes, I have noticed this. I can't rule out other factors, it is impossible to truly figure out what causes these wild traffic swings, but I suspect your activity on here is a significant factor.
I moved house earlier in the year, and what with being busy beforehand and not having internet at home for a couple of weeks after, I was hardly on here at all. Before that, traffic had been the best ever, after, well I had a similar drop to you. Something similar (though less dramatic) happened when I went on holiday for a week at the beginning of this week.
Some of the traffic lost will be from newly published hubs, and some from other hubbers reading your hubs based on your activity on hubpages (i.e. they see you participating in a forum thread or asking/answering questions and think hey I'll check them out) but that can't account for all of it. I think google probably ranks a (sub)domain by level of activity and how much new/amended content there is on the site. If there's little if any activity for a while, it might downgrade you, at least temporarily. Seems a bit harsh for being away just a few days though - could also be to do with the new Panda update. Keep writing and hopefully your views will pick up.