I think Google is just having problems today. For a while adsense was offline. I usually get between 200-500 a day but today I only have 42 impressions.
Google was having troubles earlier today with adsense, I think they were doing maintenance. Don't worry about it.
My impressions today are about 1/2 of what they normally are. Seems to happen when they do maintenance, however normally there's an adjustment within like half a day to correct the situation.