Let's be honest. There are some days when we really don't feel like warming up. When we really don't feel like practicing. Anyone who denies this is either lying or should be put in a museum.
There are many tricks for navigating this occasional problem. One that I use is to put on an artist that can do something I can't do on my instrument, of which there are literally thousands. Could be a tuba player and could be a clarinet player. I then focus in on exactly what aspect of their playing I can not achieve on my instrument and then simply try to go close the gap in the practice room.
Listening that intensely to someone else's playing helps me to regain focus and identifying what aspect of their playing I specifically want to add to my own playing helps me be motivated enough to get to work.
This is a very quick solution to a common problem that we all encounter from time to time.