Similar bouts of depression strike me periodically as well. Although I know in my head they are nothing more than chemical fluctuations in my body, that never makes a person feel better at the time. So, like Cadence, I try to do things for myself like run with the dog or take my camera to the park - anything to get me out.
Although I do appreciate roses or dinner, if I'm in a funk sometimes things like that are actually counterproductive for me. The flowers show up and I think, "oh great, I'm so obviously depressing that I've worried Master into buying me things." I start to feel like I am being pitied, and actually withdraw further into myself in an effort to make him feel like he's helping.
In truth, the greatest help he can provide is to have me do something for him - something, however small, that I can accomplish and that he can then hold me and tell me I've done a good job. I feel worth that way, not pity. If you want to take her out for dinner, great, but make it a task for her to look a certain way or do something for you and praise that. (We're subbies, when it's all about us that weirds us out a little!)
One other thing that works for me, though I've never really heard it talked about on the forums in this capacity, is for J to take me as close to "sub space" as he can get me. It's not overtly sexual, he'll simply hold me and talk while running the flog up and down my back, alternating from strokng to actual flogging. Emotions like what your slave is going through run pretty deep and, in my case, focusing on Master's voice and on the pain of the flog etc. take me down to where I can find those emotions. We rarely ever have sex during a session like that, what ends up happening is all of the emotions that are buried in me come up, I have a really good cry and he holds me. I feel SO MUCH BETTER afterwards.
Hope some of this helps, Tom. Good luck!