I think you have to battle through it, not give way I know thats hard I haves some of it, but I feel when we let it happen , we get into the habit ,so when you have had a heavy day, give yourself some rest time then put it out of your mind and get going again, I mean do not focus on the fact you are tired, sounds simple well I think our thoughts also make us feel bad, if we expect to feel worn out we will.its impossible to experience any negative feeling without first creating a corresponding negative thought.This may not work for you it has for me I dont let my thoughts dominate me, I can rest for a while and without thinking get up and get on with my life, it becomes a habit. I hope you find some answers I have been researching something similar I have recently found out I am Hypoglycemic and that makes me go up and down... Good luck