Unfortunately I sincerely doubt it has anything to do with your sitemap changes.
Seeing as how Google released a major Penguin update Friday, the fact that your rankings were lost Saturday morning seems to fit that timeline perfectly. It would be a pretty crazy coincidence otherwise, and sitemap changes truly should not affect rankings like that.
A quick look at ahrefs to peep your backlink profile and it does smell a little fishy. The growth in linking root domains you've had over the past few months has been pretty intense.. huge leap from april thru july and that's indicative of some blackhat SEO work.
Your anchor text seems to be keyed to a lot of spammy phrases like "promotional products" and **"corporate gifts."**This could also be triggering the Penguin penalties. I see a lot of links from sites like "freeseodirectory.com" and that's another red flag right there.. directory links, forum spam, etc.
Start digging through those backlinks, check your google webmaster account and watch for notifications of manual action. It still could be an algorithmic penalty even without notification though.. Just check out your SEO practices. You should know what you're doing to gain links and my guess would be it's in violation.
Good luck!
