I am so sorry. My Trace died much the same way. We went to bed at 1AM....he was fine but he wasn't fine at 7.
He was only 13 months old. For a long time I blamed myself for what I should've done, could've done, etc....it's hard not to...but eventually you have to accept it was meant to be for whatever reason.
All of us who accept the love and companionship of a pet...also must experience the eventual heartache of losing one. Unfortunately...it happens to some of us much sooner than others.
Time heals the ache but it just doesn't seem to pass quickly enough.
Take care ~