Ask HN: I've lost the ability to concentrate. How can I fix this?

I seem to have lost my ability to concentrate, work, and think deeply about topics. I can't even seem to read a book, even when I want to. I check my phone for notifications. I get anxious. Occasionally I feel depressed or hopeless. But I generally feel okay-ish, I think.

What's the quickest way for me to regain my ability to concentrate and get into states of flow?