Their third consecutive league victory on Sunday fired Dortmund into the qualification zone for the Champions League, three points ahead of closest opponents RB Leipzig, who were thrashed 5-2 by VfB Stuttgart the previous day.
"It just feels really good to get these results. We're happy that we're getting our confidence back," Fullkrug told DAZN.
But the home side failed to create much from open play and were punished shortly before the break when Nico Schlotterbeck's own goal gave Bochum the equaliser.
After halftime, however, substitute Jamie Bynoe-Gittens had an immediate impact and needed only one minute on the pitch to provide Fullkrug the assist for his brace in the 72nd.
He then completed his treble in stoppage time, again from the spot after Bynoe-Gittens was fouled inside the area.
"We didn't play an outstanding game, not a perfect game. But once again we've taken a step forward and were able to reward ourselves with a win," Dortmund coach Edin Terzi said.
Earlier, Union Berlin concluded a turbulent week, in which they had coach Nenad Bjelica suspended for three games, with a 1-0 win against Darmstadt.
Benedict Hollerbach scored the winner in the 62nd minute to give Union important three points in the relegation battle. They sit 15th, but now five points ahead of Cologne, the first team in the drop zone.
Darmstadt, meanwhile, sit bottom of the table.
Union had a tough week that started with a 1-0 defeat in the postponed game at Bayern Munich on Wednesday.
During the match, coach Bjelica hit Bayern winger Leroy Sane in the face as the player was trying to get the ball to take a throw in.
Bjelica, who watched the win from a VIP box, was suspended for three games by the German Football Federation (DFB) and was replaced by assistant coach Danijel Jumic.