Pearson was admitted to hospital after training on Friday after complaining that he was feeling unwell and the 47-year-old was kept in overnight for tests.
The former Leicester boss missed Saturday's Championship game against Rovers, with his assistant Craig Shakespeare taking charge of the team.
He was expected to be discharged later on Saturday night but his players were unable to perk him up as they crashed to defeat.
Martin Woods opened the scoring after only two minutes and although Nick Barmby equalised, Billy Sharp restored Rovers' lead from the penalty spot before James Coppinger added a third.
The Tigers have now failed to win in their last 27 away matches, a run that stretches back to March last year while victory for Rovers was there first since the opening day of the season.
Hull were caught napping in only the second minute when Coppinger picked out Woods and the midfielder's looping header found the back of the net for his first goal since last December.
Woods almost doubled Rovers' lead after six minutes but his free-kick from just outside the penalty area was palmed away by Hull goalkeeper Matt Duke.
But the Tigers responded and they were level two minutes later when recent signing Robert Koren found Barmby and the veteran midfielder produced a clinical right-foot finish from the edge of the area.
Woods was clearly full of confidence and he tried his luck once again with his left foot this time but Duke once again made the save.
Both sides were looking dangerous going forward and on-loan midfielder John Bostock was denied by veteran Rovers keeper Neil Sullivan.
But Sean O'Driscoll's side had the upper hand in the first half and they were back in front four minutes before the break when Kamil Zayatte handled in the area and Sharp sent Duke the wrong way from the penalty spot.
Brian Stock could have extended Doncaster's lead two minutes into the second half but the midfielder's shot from 20 yards out failed to trouble Duke.
Former Newcastle man Nolberto Solano crossed for Barmby but his header was comfortably dealt with by Sullivan.
And Hull found themselves further behind 68 minutes in when Woods crossed for Coppinger, who made no mistake with his close range finish.
Sharp fired in shot from the edge of the area with 15 minutes remaining but Duke made a comfortable save and Coppinger flashed a shot wide but the three goals were always going to be enough for Rovers.