Yeah, I've experienced days like that too
Usually such a blah, apathetic, boring days are due to lack of sleep or a bad, heavy meal the previous day
So, the only solution is to eat better (avoid junk and fried foods and eat more phytochemicals, antoxidants and micronutrients rich veggies and fruits) and sleep more
If you take a nap and after that you walk for a mile having a fruit smoothie afterward you will feel immediately better and more willing to go through your day
I would completely avoid playing, talking or even thinking about piano until you don't feel any better and more motivated otherwise you might end up creating a link between the apathetic feeling and the pieces you're working on
Daniel