Sick Puppy or Behavioral Issue?

Question
I have an 8 1/2 month old great Dane puppy.  Up until this point he has been an active, outgoing and well-adjusted dog.  Within the last 10 days, he began having episodes of trembling and crying while lying down.  His appetite has decreased and he acts fearful and nervous.  He also experienced two days of mild lameness in the left hind leg.  I have taken him to the emergency clinic twice and he is now seeing a neurologist.  His bloodwork and radiographs are normal.  Aside from a fever on one veterinary visit and a weight loss of 5lbs in one week there are no other "tangible" symptoms, except for what I am observing.  He has also been tested for Addison's Disease and his thyroid was checked.  He is currently on Rimadyl and pain medicine to rule out joint problems.  The next step would be a brain scan.  At 3 months old, he was diagnosed with a mild pulmonic stenosis, but otherwise has been healthy up until this point.  The big debate is whether or not this is a medical issue or a behavioral issue.  My gut tells me that there is something medically wrong with my dog, but I cannot rule out a behavioral issue.  I am worried sick about my puppy.  I have had him since he was 7 weeks old and in 10 days he has become I dog I do not even recognize anymore.  I am grateful to any advice or insight into this problem.  I want my healthy and happy puppy back.

Answer
My guess is that it is a medical problem.  It could be 'Wobblers' or OCD from a damaged vertibra from playing to roughly.  It doersn't cound as though it is an infection more a structural problem.

Sorry I can't be more help but it is dangerous to diagnose at long range.

Ken