Sounds like you have a well developed Anapanasati. This is often the reason why the mind automatically goes to the breath. With that kind of practice it is likely your samadhi is also quite good. This samadhi suppresses the hindrances, including sleepiness, causing disturbed sleep at night. This is something commonly seen with well developed samadhi states, and possibly a well known problem in those traditions that develop jhana. The solution is 1) not to meditate at night, just before sleep 2) learn to bring samadhi 'down' ie bring the mind to it's original pre-meditative state at the end of each session, by conscious control (a little 'tidying up' task), before opening your eyes and getting up. This puts the 'samadhi states away' for later use. 3) exploring, discovering and using the path your mind takes to fall asleep, consciously.