is it the winter blues? get some sunlight in the mornings. read a book outdoors or go for a walk in the park.
in terms of your game, i agree with a singles practice session. only have one or two things max that you want to focus on. major theme is just to play freely and have a good time.
also, are you watching the Australian Open? i sometimes find watching slams gets me excited about the sport. however, this won't work if you idolise a particular player and he is playing badly too.
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM