A rabbit is a prey species and therefore it is built into them not to show obvious signs of sickness. Often by the time you realize a rabbit is sick it might be too late to even help him or her. Over the years my family has lost and saved rabbits that fell ill. One helpful tip is banana.
Banana can bring a baby bunny back with a few bites sometimes! Banana offers an easy to digest quick to metabolize nutrients.
Next time you have a bunny that is feeling bad try feeding them this and see if it helps.