[Qem]

I never played any instrument, but I had the exact same experience getting through difficult stages in videogames.

[k__]

Yes, me too.

It seems to be a thing with practicing motion sequences.

[sobjornstad]

I've noticed the same thing with rote memory tasks like lines of poetry, so I think it might be a more general thing involving the memory consolidation properties of sleep, maybe particularly focused on fluency/speed rather than mere ability to recall.