>I don't believe he was sick and could not effectively lead his troops.
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Actually, Lee did suffer a great illness during the war, so great that it is said to have contributed to his death, and I wonder if so serious an event may have impacted some of the engagements.

from; Recollections and Letters of General Robert E. Lee,by his son, Captain Robert E. Lee:

Written by Col William Preston Johnson for the "Personal Reminiscences of General Robert E. Lee by the Rev. JW Jones, published in 1874. Col Johnston was an intimate friend of the General and a distinguished member of the faculty of his college. He was also one of the watchers by his dying bedside. I, therefore, give it in full:

"The death of General Lee was not due to any sudden cause, but was the result of agencies dating as far back as 1863. In the trying campaign of that year he contracted a severe sore throat, that resulted in rheumatic inflammation of the sac inclosing the heart. There is no doubt that after this sickness his health was more or less impaired; and although he complained little, yet rapid exercise on foot or on horseback produced pain and difficulty of breathing. In Oct. 1869, he was again attacked by inflammation of the heart-sac, accompanied by muscular rheumatism of the back, right side, and arms. The action of the heart was weakened by this attack; the flush upon the face was deepened, the rheumatism increased, and he was troubled with weariness and depression.

The book describes Lee's final hours: a southern poet has celebrated in song those last significant words, "Strike the tent": and a thousand voices were raised to give meaning to the uncertain sound, when the dying man said with emphasis, "Tell Hill he must come up!" These sentences serve to show most touchingly through what fields the imagination was passing; but generally his words, though few, were coherent; for the most part, indeed, his silence was unbroken.