Sunday, the billionaire entrepreneur opened up about the moments that don't end up on Instagram.

He's got the good life, right? But that doesn't mean it's easy.

"The reality is great highs, terrible lows and unrelenting stress. Don't think people want to hear about the last two," says Musk's tweet.

The reality is great highs, terrible lows and unrelenting stress. Don't think people want to hear about the last two.

A Twitter follower asked Musk to elaborate on how he manages it. Musk says he doesn't have a great solution.

"I'm sure there are better answers than what I do, which is just take the pain and make sure you really care about what you're doing," he says.

I'm sure there are better answers than what I do, which is just take the pain and make sure you really care about what you're doing

Musk has previously said that he is driven by a passionate desire to make the future better. "We are doing what we can to have the future be as good as possible, to be inspired by what is likely to happen and to look forward to the next day," he says in a recent speech to the National Governor's Association.

Sunday, on Twitter, Musk was also asked if he was bipolar, to which Musk replied, "yeah," but then he explained further, saying his psychological highs and lows are associated with actual ups and downs in his life.

"Maybe not medically tho," says his tweet. "Dunno. Bad feelings correlate to bad events, so maybe real problem is getting carried away in what I sign up for."

Maybe not medically tho. Dunno. Bad feelings correlate to bad events, so maybe real problem is getting carried away in what I sign up for

That, he says, is part of what it means to be an entrepreneur trying to change the world.

"If you buy a ticket to hell, it isn't fair to blame hell …"

If you buy a ticket to hell, it isn't fair to blame hell

Long-time venture capitalist Fred Wilson responded to Musk's tweets on his own blog, AVC.

"What [Musk] describes in that tweet is the life of an entrepreneur. And also, to some extent, the life of a VC who cares. The unrelenting stress is the hardest of the three in my opinion. Stress is part of life, we all have it," Wilson says in the post published Monday. "But starting and running companies brings stress that seemingly never stops."

It's incumbent upon entrepreneurs to take care of themselves, he says.

"Managing that so that it doesn't eat you up and mess up your relationships is super hard," writes Wilson.