Sandhausen took the lead 2-0 after goals by Julius Biada and Gerrit Nauber. With the 58 minute mark, the Swedes got the ball just outside the penalty area and shot the goal at the keeper's right post.
Four minutes later, Guidetti was replaced.
With less than ten minutes left, Philip Turpitz extended the lead to 3-1 for the home team Sandhausen.
The goal was Guidetti's first since the restart of the 2. Bundesliga and second in eight games since he was loaned to Hannover from his Spanish club Alaves.
With the loss, Hanover was passed by just Sandhausen and is now eleven in the 2nd Bundesliga.
The match was played for no apparent reason without audience.