Kal will be 9 in January.  Last week while walking through park he suddenly started limping.  His left rear leg held up off ground.  Thought it was a Sand spur, a common thorny seed occasionally picked up on foot, but no such luck.  Then thought perhaps a metal or glass sliver, but later under intense light could find nothing & no reaction to touch.  Poking & prodding ankle, knee & hip also drew no reaction. 

All I could common up with is; day or 2 before he'd slipped on slick kitchen floor when he tried to get up too fast & sprained something, but had a delayed reaction?

He has always been prone to leg tremors, especially when excited.  Vets never concerned about it, did mention onset of arthritis.  But tremors have increased.

Gave him aspirin which seemed to help & over 2-3 days he improved, but a week later is still plainly weak.  Will not jump up into truck anymore, needs boost.

Been Googling the topic, but haven't come up with anything that clicks.  Should have been protected from Lyme's while in NY, where ticks were scarce, but fleas epic. 

Any ideas before I make appointment?