I don't have bipolar, but I have depression, and I haven't had a bad one in awhile but I'm getting into another one now I think. I can't take SSRIs so really exploring medication for me is not an option. I am on Wellbutrin and Epival but really I'm pretty sure they don't do ****. I want to come off of them entirely and find an herbal/natural way to approach mental health (acupuncture/massage/aromatherapy/herbalism/meditation/mindfulness/DBT/whatever).
I do what you're describing. As someone else mentioned, it helps calm me down. Oddly enough, when I'm planning my death I'm not actually thinking about carrying it out. I'm just locked in a fantasy like any other fantasy, and then I usually end up forgetting what I was thinking about. I don't think there's anything weird about it at all but if it gets to the point where you're like 'Hey that sounds like a good idea, think I'll try it' you should probably call 911 or suicide prevention or a crisis line or something.