Well that stinks. Sorry to hear it happened so quickly. We all know our pets will die one day but to have it come on out of the blue like that is tough.
My buddy, also named Jake, is an old fellow himself and has not been acting his normal happy self for a few days, seemed a little better yesterday, but I know his days are numbered, and I know that soon, I'll be forced to make that same decision. He's still happy enough that I'm not ready yet, but once he is at the point where his happiness is no longer there, I know it's going to be the right thing to do. He just turned 10 last week, but he's a 150# lab/golden mix that has no doubt aged a slight bit prematurely d/t the weight on his bones, but he's truly not a fat dog, just a massive almost to the point of having a St. Bernard's structure animal. Sorry for your loss as I'm sure your Jake was as special and meant as much to you as my Jake does me.
I am so sorry for your loss and kmow exactly what you are feeling. Seems like we get a lot of these threads. Before we found out about our dog, I posted another poem about my Lab Domino and now this. 081313 we had to make the same call you did. It came out of thr blue too. Our Shawna was just six and was our kid, buddy and constant companion. She had lung cancer that was inoperable. I'm trying to keep it together but my wife is still pretty broken up. Anyway I hope you can find some peace and remember the good times. Feel free to change the name and picture. My screensaver Surf fishing with Shawna