Do you have a lower traffic when celebrating your thanksgiving day? or fewer visitors came to your site during the last week?
Obviously this depends on where the majority of your visitors come from, clearly if they are mainly US based then holidays such as Thanks Giving will affect your visitor numbers. Generally, because many people do a lot of their browsing at work, if they're not at work then there's a lot less browsing, and in turn a lot less visitors to your site.
That's probably the answer, we have a very low traffic during the last week, but the situation is still not good on Monday..