Hm. If you have the option, perhaps having some form of entertainment going while you settle in could help? If you were distracted by videos, shows, or music while brushing your teeth, it could be harder for negative thoughts to settle in. That's what I do.
On the other hand, I also get drunk 4 nights a week. But this works for me either way, I swear x) .
Like I said, see about getting properly evaluated if you can. Being bipolar is certainly worse than not being bipolar, but it's not necessarily the wild roller coaster often depicted for every person who endures it. Case-in-point: I have the condition myself, and outside of one relatively recent trauma-induced breakdown, I've always been pretty stable .