I find that Google Analytics is not useful for following TODAY's stats. There are periodic lags and often an hour or two or three will simple not be reported, only to show up two days later.

So traffic may not be down. It just may look like it's down.

AdSense stats seem to be normal.

According to my AdSense reports, compared to yesterday my site's traffic and ad impressions are the same today as yesterday, clicks are down, earnings per click are higher, and earnings are about the same.

Everythng for me is up. eCPM, CTR etc etc. I nearly always get a good spike towards the end of the month. I assume Adwords are using up peoples monthly spend and you get better ads.