I started my spinal breathing practice about three days ago. The past nights my dreams have been so lucid , like I'm really there(maybe I am!).I also noticed that my internal clock is coming up short on my post meditations. I've rarely fall short of at least 20 minutes or more, however I've been doing 15 minutes. I had one of my best days at work in a long time, great energy, good attitude, smooth flowing work effort. Looking forward to continuing to supplement my year long meditations with this new found practice.
I think that the dreams have nothing to do with breathing. That is the whole point meditating cleaning your innerness. No mantra more headache. Breathe after meditation? Meditation after sleep changing habits? Just meditate.
I just use a timer so that I know that I have done 20 minutes. Inner clock is fine if you can rely on it, but for learning I feel that it s good to time the practice. That said, if 15 mins feels right and the rest of your day is good then that is proper self pacing. The key is consistency. As far as dreams or other phenomena, they come and go, probably best not to dwell on it too much as being a result of meditation because that will change in its own way over time.
My friends talk about meditation but they do not want me to meditate with breathing first. It is my breath and my moment and maybe you have people wanting you to do this do that.