The mind can only notice previous mind moments. In that sense it's always retrospective. Something has to already exist, otherwise it can't be noticed. Right? But, the arising and passing of moments is incredibly fast. A teacher once told me that it's several thousand mind moments per second. Basically, you're always looking back into the past, so to speak.
So, sayings like 'becoming aware of the Now' or things like that are highly misleading. But, I might digress here.
And yes, it is possible to te aware when in a state of flow. It's two different things. There is 'being in a flow' and there is 'being aware of this or that'. Two different things equals four different possibilities:
1) Being in flow and being aware of it
2) Being in flow and not being aware of it
3) Not being in flow and being aware of it
4) Not being in flow and not being aware of it
Hope this helps.