Hello A A,
Your post got me paranoid and I went around to all the different online tools that will check rankings from different data centers like http://dccheck.com/ . I got a wide variety of responses from these tools and it made me wonder if they worked at all. I also don't have any hard answers for you and it sounds like you may have had some trouble in the past;however it is possible you are freaking out about nothing. Is your traffic stable? You could check google analytics and filter for search traffic then your keywords. From there go and check the geographic map the traffic is coming from. Compare a current time period this way to a past time period when you know you were ranking well. It it is not too different, maybe there is nothing to worry about. Does that help?