I'm pretty disciplined. I go into my office at 8 every morning and I'm there until 12:30 Monday - Friday. I'm a morning person, so I do much better with that kind of schedule.
Yes, I don't know any writer who hasn't. I do a couple of things, one is to take out a pad of paper and write in long hand, rather than on the computer. It makes me think in a different way. Another is to read something else I've started. maybe from years ago. I never work on just one book, so I can hop around and take time my mind to a new place.
Actually, learning to read. When we downsized and moved to our current home I found a manuscript I wrote when I was seven. Books have always been my friends.