How To Overcome The Loss of Flow in Writing

I hear some self acclaimed writers say that writing is like a second nature to them and when they start, they never wanna stop! Naturally, I scoff at these brutes, but within me I feel like I'll never be as good as them. Has this ever happened to you? A few minutes after you start writing, you pause to reread what you've written. You adjust something here, polish something there, delete a sentence. Suddenly, you find it hard to start writing again. You've lost the flow.