I think we all have days which aren't particularly bad or stressful, but are simply "blah". You get out of bed without your usual spirit of enthusiasm and energy; nothing seems worth doing and all you want is to crawl back under your blankets with a good book and a cup of cocoa and curl up there for the rest of the day.
I have that from time to time, and developed a simple strategy of dealing with the "blah"s when they come:
1. Do something. Even if it's a small and simple task, it will get you started and – hopefully – motivated. You can start from the quick and easy chores, to give you a feeling of accomplishment, or from something you particularly like. For me, it's usually laundry: washing, sorting and folding, or ironing. It usually gets me in a working mood.
2. Brighten up your background. Whether it's putting your favorite music on, lighting a scented candle or drinking tea from an especially pretty cup, even the little things have a potential of cheering you up.
3. Take it slowly. It just happens that on some days we aren't quite as productive as we are used to. Maybe your previous days have been so packed with activities that you just need to rest, or maybe a cold is approaching. So just make sure the basic tasks get done, and leave the rest for another day. Or devote your time to less straining tasks, like writing out your shopping list, planning your menu, making phone calls or catching up on your correspondence. "Blah" days come and go, so why not just take the opportunity for a bit of quiet time?