Bathroom Breaks are being used as strategic tactic to break momentum in matches. Most tennis players would agree that there is rarely a need to use the bathroom once the tennis match starts. During a match, there is, typically, a greater concern for water replacement than excessive urination.
On rare occasions, diarrhea may be a factor. Diarrhea might be considered an acute injury. Urination is not. Perhaps the best rule for bathroom breaks may be to only allow it at end of split sets.
In a comparison, it would be unimaginable to see the situation in a boxing match where one boxer has delivered enough body punches to have his opponent leaning into the ropes - ready to submit. Then the player who is under duress, suddenly call for a trainer to give him medical attention or to call for a bathroom break. Likewise, in a tennis match, it often takes over an hour of steady shot selection and pressure to weaken an opponent.
The current rules for tennis should be adjusted to eliminate such disadvantages for the player that who has diligently worked to gain momentum.