As often as not when I access the site after a long time away, I get some vote within just a couple of minutes. It's almost as if someone else notices that I'm back on the site. Does the Community User nudge some of my questions/answers when it notices that I've connected again after a layoff?
Most likely this is just coincidence or somebody is messing with your psyche. I'm going to chalk it up to coincidence--you have a huge number of answers, and people are browsing them all of the time. Given that I have a fraction on your work and I get random upvotes on old answers, I can only imagine that this is a much more frequent occurence for you.
The paranoia comments reminded me of one of my favorite exchanges in Catch-22 by Joseph Heller that I felt like sharing because what the hell. It goes (paraphrased):