12 year old labrador retriever

Question
As an extra large dog (125 lbs) he is considered old and we have been seeing his health decline.  However, recently he started stumbling more and yesterday he wasn't moving much at all.  Today it's as if his muscles in his legs and neck have spasmed and won't relax again.  He makes not effort to move on his own.  Is it just a matter of time for him as he does not seem to be in any pain when we move him.  He ate and drank water with our help in controlling where his head and neck went.

Answer
I am sorry, I didn't see the question in here about time. It sounds as if he is at the end indeed. Most Labs rarely even make it to 12 yrs old so he did well. My folk's Lab just lied down like yours and finally went into a comatose state until they took him in and had him put down. He wasn't in pain either but they couldn't bear to watch him.
If your dog is not in pain or discomfort there is no shame in a natural death.
He sounds like he has some sort of a paralysis going on but from what I couldn't tell you. It could just be that everything is shutting down.

I hope that everything goes smoothly and quietly for you. Please accept my condolences when he passes but you gave him a long, healthy and happy life.