Being dead at one's own funeral is not unusual, but waking up at one's own funeral after being mistaken for dead, then actually dying is definitely unusual:
Fagilyu Mukhametzyanov, 49, was mistakenly declared deceased by doctors [...] But she later woke up - in a coffin surrounded by sobbing relatives. She started screaming after realizing she was about to be buried alive.
Mukhametzyanov, a resident of Kazan, was rushed back to the hospital where she was declared dead -- this time for real.
From the NY Daily News: Link