A week before xmass my normal sites slowed and my entertainment site got busier... now it's going back to normal... of course people sleep later and all...
Many businesses online and even brick and mortar stores always have seasonal effects depending what the content or merchandise is. Keep tracking the moving averages of your traffic and if you see continued dropping over a period of time (several weeks), then there may be another cause (perhaps rank changes in search engines from a google dance, who knows). Anyway, I hope for the best for you. : )