You are seeing a prime example of why Alexa rank is worthless.
If the number of visitors to your site has stayed the same, why do you care what changes might have shown up in this useless made-up number?
Why it changed... most likely, someone who was visiting your site uninstalled the Alexa toolbar. Or maybe it's you: if you have the toolbar installed and just stopped visiting your own site so often, that could have caused the change. I once "improved" my Alexa rank by several hundred thousand points simply by installing the toolbar and visiting my own site three or four times a day for a month.
See, that's how the application determines your "rank": by counting the number of visits from people who have their stupid toolbar installed. (Including you, the site owner.) And since the vast majority of real people don't have the toolbar installed, the Alexa rank simply measures the number of visits from a tiny minority of people who are either (1) too oblivious to realize they have the toolbar installed, (2) too technologically challenged to figure out how to uninstall it and/or (3) too obsessed with Alexa ranking to understand they're wasting their time with trying to influence it.
Want to "recover"? Make sure you have the Alexa toolbar installed and start visiting your own site several times a day. Recruit a couple of friends to do the same. It won't help you make any more sales or do anything even remotely worthwhile for your site, but if it makes you feel better, go ahead and waste your (and their) time with the project.
In summary: The Alexa "rank" is a meaningless number. There is no reason I can think of to even check this number, much less worry over changes in it. Focus instead on metrics that actually mean something (number of visitors, conversion rate, revenue or leads generated) and stop wasting time obsessing over useless "rankings" that have nothing to do AT ALL with anything worthwhile.