Are there unnoticable effects of cooked food going bad?
Yes, some bacteria do not produce immediately visible results, and molds are not visible until they reach the stage where they begin to produce their fruiting body (the part you see, is actually the organ they use to reproduce).

There are of course some signs that the food is irreverably compromised including:


Off smells, especially fermented or putrecent odors
Off tastes
Sliminess
Visible mold
Bubbles


Still, you cannot count on one of these signs being apparent.  You will have to assess your own tolerance for risk.