It sounds like we're around the same age, both a few years out of a PhD (mine was in bio). I'm happy to email/talk 1-on-1 with you about this:

1. Do not continue down the academic path. Your mind and body are clearly telling you to stop! Instead, start applying for jobs as you wind down your ongoing projects.
2. Probably don't start a business right now. Not unless you have a major technical edge in a lucrative area and a suite of business-relevant skills (I couldn't infer this from your post).
3. If your internships were at large/established companies, I would be unsurprised that they went poorly. There are stark cultural differences between academia and the corporate world.
4. Consider joining a startup. Culturally, this will be a smoother transition than to big corporate. You will be paid much more than you are as a postdoc. The people around you will generally be happier than your academic colleagues. And you'll build skills that are relevant to starting your own business one day.

Academia is wonderful in many ways, but it teaches people that life is linear, which is a damn lie. Life isn't linear! You have decades ahead of you that will be filled with personal growth and bringing happiness to other people.