I've found Bipolar Disorder responds very strongly to both internal and external stimuli. Depending on whether you are diagnosed with type I or type II, there are different things you might want to focus on more than the other, but with both bodily consistency is key: things like good nutrition, good sleep, and regular bodily movement can really help make sure your body is running as optimally as it can.

For me personally, it's a bit complicated because I also have another disorder called Borderline Personality Disorder that mimics Bipolar in many ways, but is a bit different. I usually end up in the hospital for things related more to that, but the times I have been in the hospital usually start when I get into patterns of isolation, avoidance, and either sleeping all the time or sleeping too little.

Eventually I'll potentially notice an increase in negative thoughts about myself and the state of my life that become hard to disengage from, eventually leading to intrusive thoughts of self-harm. I might also notice becoming more wound up, having speeding thoughts or racing thoughts, and being so exuberant it scares the loved ones around me. I'll stop wanting to sleep, because I am "enjoying" life too much to bother with it, which is always a mistake. For me these states usually become "mixed" and that's honestly the most dangerous time, because when they get bad enough there is the desire to hurt myself and also having the energy to do it.

That's my personal experience. Everyone is a little different, but I have noticed things like these are quite common for Bipolar people.

Hope this helps you. Remember, the hospital is a place to regulate and stay safe during a crisis. It's there to help you, even though I know many, many times I've personally hated going because I felt, internally, it was somehow a moral failure, but it's really not. Everyone needs help sometimes. People with physical illnesses sometimes need surgeries or hospitalization, and it's the same for people with mental illness. No shame in that.