Rather than make the whole day bad think in terms of moments. This is a bad moment, that was a bad moment. Even if the moments are hours if you have 5 minutes of good it's better. Also, try to do something to make you smile, even if it's just smelling flowers, flipping through magazines or going for a walk.
Or, go in a room and have a good cry. That works too if you can make yourself cry. If not, it's anger and not sadness and that's a little better.
As the moments carry on things will brighten up.