This is something we all do not want to deal with,Just loosing Anna only 2 weeks ago.
Thunder will let you know,It may not have to be a whimper,But just that look in his face.

That is how i new Anna was ready she gave me this look that i have never seen before.

Maybe a vet visit?Just to have the vet go over Thunder and see if everything is ok.

Like my mother said to me about Anna there is Quality and Quantity to life.If they have no Quality then it is time to make that unselfish decision.

I will say extra prayers for Thunder,IT may not be anything,You watch an older lady or man,They are not as quick as they once were,It could be he is just really feeling his age and will slow down on some things.

Hugs to you,I hope the best for you both.