What Causes Fluctuations In Heart Rate While Having Afib?

My husband has afib. His heart rate goes from 32-45-55-36-42- All the time. He has asked his heart rhythm dr. about this. He told us there was nothing that could be done.He is on a blood thinner.It is affecting his daily life. If he sets down at any time he falls asleep. His moods go up and down to the point of not wanting to be around anyone. He is a vary out going person so this is not normal.I guess we just need to know, if we have more options we can look into?