Dude, leave it hanging up as a jacket. You don't want to keep the down compressed while you're storing it. That'll decrease the loft of the down in the long term.

Hanging! The down's loft will be restored quicker. If it seems less lofty after a while, wash it using the tiniest thimbleful of detergent, making sure that it all gets rinsed out. Ideally, do so in a front-loading washer. Dry it then at low heat, and throw a coupla clean tennis shoes in with it to pound up and loft up the down. As long as you get all the detergent out, there's nothing you can do to down that can't be restored by a washing.

I think Peter below meant tennis balls, not tennis shoes into the dryer with it.