I've not had experience with this post-amputation, but I've had first-hand experience with the demon that is tick paralysis.

Why did your vet think this might be the problem? Did you remove a tick from Darby? If this started about 5 days ago and Darby is alive, it likely is not tick paralysis, unless you removed a tick. Tick paralysis is progressive and eventually paralyzes the muscles controlling the respiratory system. Five days is a long time for a dog to have tick paralysis and still be around.

When our dog had this several years ago, we'd scheduled a  home euthanasia because we thought she'd had a stroke. We watched the paralysis run its classic course: hind limbs first, then spine, then front limbs. Over the course of a couple of days, she lost the ability to lift her head and to swallow. Her bark became hoarse (classic). She choked on water that she tried to drink, as her esophagus was paralyzed. If your dog's symptoms are not progressing like this, it likely does not have tick paralysis. (I found the offending tick hours before the vet was to come euthanize our dog.)

I think the others are right and Darby just needs some time. This is a major surgery, and not every dog recovers at the same rate. If you look around here, you will find several who tanked hard after surgery and needed a lot of extra TLC to be up and at 'em again. Hopefully that's all Darby needs.

Shari