Fatigue
Your heart works faster than it should when you have atrial fibrillation. Unfortunately, an increase in heart rate does not translate to more efficiency. What happens instead is that the efficiency of your heart drops [6].
When your heart overworks itself, you use more energy. This can reduce the energy available for you to perform other tasks and leave you fatigued [7]. The drop in efficiency also means your heart is not able to fully utilize the oxygen you breathe in. Your muscles depend on oxygen for energy and its absence may also contribute to fatigue.
While fatigue is often described as tiredness, they do not mean the same thing. Fatigue is a more intense and chronic type of tiredness. When you are tired, a nap may rejuvenate you. Rest often does not improve fatigue.