Because of you mentioned sleep-focused meditation, I’m think you aren’t referring to mindfulness meditation.

Maybe you’ve been practising some kind of Zen-Bhuddist meditation, I’m not sure, I’ve only ever spent time practising Mindfulness and Loving Kindness.

Also, maybe we’ve got different definitions of flow state.

What I’m referring to is the feeling of having completely immersed yourself in an activity, to the point where you aren’t verbalising thoughts.

Being anxious during a flow state is a bit of a paradox, as anxiety is a symptom of complex thinking, which is what mindfulness aims to alleviate.