If you try logging back on, are you seeing anything suspicious?
If everything looks fine (i.e. you're stil lat Vorkath, or at Death) it could have been a disconnection caused by unstable internet connection at the time of fighting Vorkath.
You can learn more about resolving connection issues here:
Common connection solutions
Life is like a camera: Just
focus
on what's important,
capture
the good times,
develop
from the negatives, and if things don't work out,
take another shot
!