Fatigue: exhaustion, extreme tiredness,  and the feeling of listlessness as if you have no life force. This is what would happen right after I would eat when my system was teaming with candida yeast. Sometimes my lunch would put me directly into sleep. My daughter jokingly uses the term, “food coma” when she eats too much. I would say that is a literal description of what happens in extreme cases of feeding the beasties. It is unlike weakness as a strong person can have the feeling of fatigue. Fatigue can have physical or mental causes. Physical fatigue is the inability of a muscle to maintain optimal physical performance.This could occur after  intense physical exercise, however, if there does not seem to be a logical reason to feel fatigue, it could be due to anemia which is common in people with impaired digestion. 
If you are experiencing fatigue consider that nutrition could be playing a role. When gut flora is imbalanced the pathogens have a way of taking over. According to Dr.Campbell McBride, some of these pathogens thrive on eating the iron in our blood causing the symptom of fatigue.