Sometimes (and almost certainly in this case) this is a serial down-voting issue - did you upset anyone or get into an argument?
On the plus side, if the same user down-voted a bunch of your posts in a short time frame, this type of activity usually is caught by the system (and I believe the script runs once a day). Check back tomorrow and see if your reputation has been restored (your reputation history will say something like "Serial down-voting reversed").
That said, it could be just that you have bad questions, and the timing could be coincidence or it could be someone who visited your profile and then went to each of your questions and found them lacking. Hard for any of us regular peon users to tell, really. I do notice a common trend (not in every single question, but several) that many folks look down upon: you don't show us what you've tried, so your questions kind of come off like "gimme teh codez." Not enough for me to also down-vote, but down-voting is a very subjective thing.