I have the same issue with my 13.5 year old Springer Spaniel Vegas.  He had his right front leg amputated third week in April.  He is not walking very well and is falling a lot.  I don't know if it is an issue of weakness or coordination.  I have been taking him to rehab every week after removal of staples (three times so far as he had a setback and had to have the wound resutured) and they had him swimming but last week we couldn't go.  He lays around most of the time and he can get up on his own but mostly won't.  Not even for a treat (but I know it can be an issue of me picking him up originally and him barking for me to pick him up instead of getting up himself). He was able to jump from the house to the porch and now he can't and splatters - the step is little higher than ordinary clearance.  When we go for a walk he will hop OK and all of a sudden splatter on concrete.  I mostly walk him on grass but we have to cross the street to get there and even though I am trying to be careful he always falls when I least expect it.  He was very strong before the surgery and that was the main reason why I decided to go for it.  I am really sad and depressed because it breaks my heart to see him flail and fall.  He had a terrible time at the beginning for about 10 days.  He was extremely frightened and depressed.  At first he could not even stand on his own - three days.  Then he started to hop a little but it was still quite bad emotionally.  After about three weeks he perked up and everything started to look up but it seems like a set back now and I am scared.  I would really like to hear advice that you get because I need it too.