Racing thoughts is a common symptom of BP (as well as ADHD which has a high comorbidity with BP), and when you are in a quiet bedroom with no other stimulation, your mind is the only thing left, interacting with itself.

I used to have this issue constantly, until I was finally put on a mood stablizer (Trileptal), which has helped immensely in reducing the night-time racing thoughts. I end my evenings with reading books, and when I want to finally go to sleep, I do a sort of meditative breathing to relax my brain and sink in to slumber. Focusing on your breath, deep and healing, is a great way to naturally relax yourself. I would also recommend getting a blue-light filter app on your phone, that you turn on before going in the bedroom. This filters your screen so that your brain isn't tricked in to "seeing daylight" (more info here: https://www.health.harvard.edu/stayi...as-a-dark-side )

I also have ADHD and have been on adderall for the last year and a half, which I take once a day in the morning. By the time I've had dinner, the adderall isn't affecting me much anymore so it does not interfere with my sleep. It also helps calm the racing thoughts throughout the day and allows me to focus better on my work.

You can also look in to melatonin as a sleep aid, but be careful with the dosage, too much and you will just wake up groggier than you were before you went to bed. I try not to use supplements or meds for sleeping.