conversions fell down in a disasterous way

[Yauhen]

According to my statistics, I used to have 1:400 through last 4 months until last week. Last week I made only a few sales with average conversion around 1:1500.
The amount and the quality of my traffic didn't change whatsoever. I have the same amount of hits and unique visitors as I have been getting for the last 4 months, but now I have almost no sales, while I always used to make 1-3 sales a day for those last 4 months.

Is there anyone around, who has been experiencing the same sort of problem recently? I wonder what the hell is going on. Is it a sort of seasonal shit or is it the shit that is happening only to me?