Bipolar business owner here. Staying centered and level in the face of business ups and downs has been difficult. Very difficult at times. My reactions to stress and difficult situations, to successes too, are often imbalanced. Still I've remained successful. Here's how:
Talk therapy. I see a therapist weekly to keep the window's clean. To validate that what I believe isn't exaggerated by my varying states.
Medication. Very low does Lithium every night.
Sleep. I make sure I get it.
Exercise has been tough to execute on, but is proven - as much as meds - to help with bipolar and GAD.
Meditation I try to do once a week as part of yoga. I find it helps.
Family and friends who understand and can be supportive also are a huge help... but are often in the minority of people I know.