I can't believe I am reading this!
I fell a little in love with Max just seeing his pictures and video. I can't imagine your heartache after having that darling little imp for five days.
Please, please try not to imagine the worse, love on him and wait and see what the results indicate. You've done everything you could at this point. You'll make yourself crazy with fear and grief. With a yorkie, the first thing that comes to mind for many people and I am sure most vets is LS. But hopefully it isn't LS or anything else serious.
Max is in our thoughts.