One of my muscovy drakes often rests with his neck stretched out like that.  It was his preferred position as a duckling.  He used to rest his neck along the back of another muscovy drake, but hormones kicked in in January and they are no longer close buddies.  Instead, he [and lately one of my pekin drakes] comes and rests their necks across my lap when I sit on the back steps hanging out with them, and then closes his eyes. 
So, nothing to worry about with the posture. 
Both my pekins drakes are air headed but very sweet with it.  They are slow to learn anything.  The smaller one thinks he is alpha male -- he is half the size of the muscovies -- he is not alpha male, just noisy.  The other keeps fighting with a muscovy that can easily turn him on his back and stand on him.  The muscovy learnt within a couple of weeks that I do not want him fighting with the pekin, and the muscovy just stays away from said pekin, while being good buddy with the smaller, loud pekin.  My larger pekin is the alpha male and tends to stand aloof from noisy pekins and the other drake.  But he has lost his chest feathers as the noisy pekin comes and pulls at his chest feathers.  Bare chested pekin also learnt very quickly that I don't want him fighting with the little pekin even if the little pekin pulls out his chest feathers. 
So, in my experience there is a lot of air headedness around in pekins, but mine are sweet ducks that like being around people, stroked and petted.  Muscovies, in contrast, can learn quite profound behavior changes and quickly.  [My bigger, alpha male, muscovy is also a great soft lump of duck with me: he really loves being petted and pokes me when he thinks I am giving the other ducks too much attention that should be redirected to him. The second muscovy drake emphatically does not like being petted, but wants to hang around with me all the time: he spends hours each day on the back steps peering in through the patio doors, looking for me.]