Mirko Slomka’s side remain in the relegation play-off place with only three games remaining after a 3-1 loss at the Imtech Arena on Saturday.
Police had to intervene as around 70 Hamburg supporters reportedly rioted following the club's eighth home defeat of the season.
Ivan Perisic opened the scoring only two minutes in and further strikes from Kevin De Bruyne and Ivica Olic heaped more misery on beleaguered Hamburg, who will have taken little consolation from Ivo Ilicevic's goal 13 minutes into the second half.
Defender Westermann was at a loss to explain the latest defeat and knows the outlook is bleak for his side.
He said: "It's incredible - incredible. If you make as many mistakes as we did, then of course Wolfsburg will punish you.
"We just invited them and that makes it even more frustrating. I just can’t understand it.
"This defeat really hurts. Our destiny is no longer in our own hands."
Slomka's side face Augsburg next weekend before hosting champions Bayern Munich and then travelling to Mainz on the final day of the season.
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