VOODOO DOLL?

So, I decided to run outside yesterday for the first time since I injured my right knee and all was going well. No pain in the RIGHT knee 9km, 10 km then around the 11 km mark....BAM! Pain! A 7/10 pain in the LEFT-yes, the LEFT knee!! OUCH. It was like someone decided to wake up on the wrong side of the bed and stick a pin in my voo doo doll! I managed to push through and complete my 19 km but today I am paying the price for it. Is this what everyone means by "getting old"? If so, keep it to yourself. Any and all sympathy comments are welcome :)