I guess that depends on how severe the lack of mood was? If it was just 'nah, don't much feel like it', some really good domming usually gets me right back into the mood. In fact, I myself am pretty amused at how easy it is. A few words by him, or a task or two... that dom-look would probably work as well, but ah, the limitations of online D/s.
However, if it's the really really bad mood, like if something really terrible happened to me during the day and I am really upset or angry, I certainly don't need a demanding Dom to add to it. I'm sure most subs here would require gentle care and compassionate understanding. And believe it or not, that can actually be done in a firm Dom-ly way, and be the more comforting for that.