I'm not sure you really have any sort of problem at all.  Unless you have seen a fall in traffic/ranking etc then I wouldn't worry.  DA calculations seem to lag what Google is doing anyway, so if you have not suffered in terms of traffic/ranking then I wouldn't worry at all.

DA is just an indicative metric about your domain, the end goal is conversions, so worry about it if those are hit but otherwise - stay calm and carry on (I should get that on a T-Shirt or something!)

Gary