What is Macbeth's reaction to Lady Macbeth's death?

When Lady Macbeth dies, Macbeth is faced with his own mortality and contemplates the brevity of life. 

When Lady Macbeth dies, it is right before the big battle between Macbeth's army and Malcolm's, because Malcolm is coming to take his rightful place as king.  Macbeth’s mind is full of self-doubt.  Lady Macbeth's death is a result of her guilt at her part in having killed King Duncan.  She lost her mind at the end, imagining that the blood was still on her hands and she could not get it off.

Macbeth’s reaction to his wife’s death is to say that she should have died “hereafter.”  In other words, he wishes she had lived longer.  However, he goes on to ponder the brevity of life.

Out, out, brief candle!
Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more: it is a tale
Told by an idiot, full of sound and fury,
Signifying nothing. (Act 5, Scene 5)

Macbeth is saying that life is so short as to be almost meaningless.  This is an important speech for Macbeth, because he is pondering his own mortality as well his wife’s.  He is about to go into battle.  He is worried about how effective he will be in this battle.  The predictions of the witches have been contradictory.  He was told he was invincible, but also to watch out for forests and Macduff.  He was also told that Banquo's sons would be kings (which was the second time that prediction was made).  Macbeth doesn't know what to make of it, but he is worried that his life might be coming to an end too.