Can't Stay Awake

It has been a full day and I just now had the opportunity to sit down and work on math.  It is a new chapter today.  I was hoping I would pick it up quickly and be able to knock out the assignments but I am way too tired.  I can't stay awake.  I've been working on the math for the last while and I can't make heads or tails of it.  Because I am so tired I am having a struggle.  I just need to sleep on it so when I look at it and practice it can begin to make sense.  Must rest.