That happens to me mostly when I don't have a band or done other means in playing with other musicians. I've gotten better with playing without a band (due to the pandemic halting band activities) but I still have to motivate myself to work alone. I always feel better once I play. I always have musical ideas, do my motivation for working alone has become creating a frame for a new song or an entire song when I sit down to play. I now have hours of musical ideas to pitch to different projects.