It's when you are out of breath, and cant do anymore ,and suddenly with inspiration you can...

O.K its really just a fancy name for a tool that enables you to rearrange your points, in case you can do better.

So just like above really.

There is much speculation , like in the rest of the game, about the best way to gear up and what points to add where and when.

How do I get more "second wind" to change my points in HH?

They are one of the items you might find in the helheim store.

Its possible you might be lucky enough to win one there, other than that its down to availability within other areas of the whole game, and probably variable by player.