Metalface Mark, you have my sympathies. It is never easy, Tilly lived a good full life, that is the main thing, just remember the good life you gave her.
I lost my young dog on 1st August 2014, it is only now I can talk about it or put it on here. He was not even 18 months. We were over the park and it was a Friday so everyone in good spirits and he was running around playing with his mate perfectly as normal.... Then all of a sudden running right by my legs he stopped and pounced up on his back legs and fell over backwards and started to have what looked like a fit. He was shaking a lot and he started crying as he was shaking.... Little dude died right there in my arms at the park that day, lasted only about 10 seconds but felt a lot longer at the time. He just gave out, shaking and crying then boom, gone.
I will never ever get the image out of my head, his eyes, the crying, carrying him back home and there was just nothing there. It was absolutely horrific.
It was massive heart failure, we knew he had a murmur from birth but had it checked many times and the vet said with absolutely no untoward symptoms being shown, proper growth and very good health it was very unlikely to cause an issue.... To the day he passed, there was never an example of warning or tell tale signs, he was perfect and healthy in every way, then boom, out of nowhere in the space of 10 seconds he is ripped out for your life forever.
He was a show dog, my ex had started wining with him, he was only getting started, had a full happy life just waiting to happen and 18 months old and is gone. Nothing deserves that, he didn't even get to live. So honestly people, just make sure the 10-15 years you get are happy ones for them and just rest easy you gave them the life and love they wanted because at the end of the day, to the dog, its master is its life and soul and not another thing matters to them so long as you give them your love and appreciation.
All the best.