Adsense does not guarantee constant earnings or a constant rise in earnings. It depends on many factors including the websites traffic sources, the Adwords advertisers, the competition for the keywords, your keywords, the ads the visitors click on, certain internal Google factors and a lot more. I used to view my stats several times a day and panicked whenever I saw a drop or a bad performance. It’s only natural that some days perform better than others and you have to live with it.