A bearded dragon stops eating for two reasons: either it is in brumation, which is just part of its hibernation cycle, or it is in discomfort. In order to figure out which reason is the cause, an owner should keep track of other possible symptoms or take it to a veterinarian.
According to TheBeardedDragon.org, one main reason why a dragon stops eating is because it is in hibernation. Each dragon responds differently during hibernation. Some stop eating, take long naps or sleep during the entire cycle. It is important that as a bearded dragon enters hibernation its owner still regularly feeds and waters it whether it has an appetite or not because a dragon often rouses itself from hibernation long enough to eat and bask in light. Also, it is important for owners to leave the dragons alone during this period.
Another reason that a dragon stops eating is because it is in pain or discomfort. If this is the case, an owner needs to be aware of other symptoms of pain, such as low energy, mood swings, swollen body parts and abnormal movements. In this case owners need to consult a vet right away. Bearded dragons also tend to behave strangely during breeding and shedding season.