Not swayback or he would not have recovered totally
Yup, swayback gets worse not better.
There is a thing (I call it 'flopbot' - not sure if it has a technical name!

) where the lamb can't stand at first; I have always assumed it's to do with being born a little premature. These mostly do recover, sometimes within a few days, one I had never stood for the first ten days.
Swayback usually doesn't evidence straight away; it kicks in as the lamb gets heavier and its skeletal system can't manage the increasing weight. They tend to sway from side-to-side at the backend, rather like an animal recovering from an anaesthetic. They don't get better but with care you may be able to rear them to a useful size. They'd struggle on a trailer ride though, and putting them in a wagonload of lambs would be a death warrant, so you have to think about how you would get them to slaughter or get them slaughtered on farm when the time comes.