I have both personal and professional experience with dehydration and
headaches.  This was a common problem for me while pregnant and nursing.
 Keep those fluids going, especially in humid weather. The old eight glasses
of water may not be enough.  Have the client drink until her urine is almost
clear.  She will need to keep fluids at bedside and drink whenever she wakes
up at night.  A few juice boxes in the night stand may do the trick.  These
headaches are not true migraines.  They hurt like crazy, but are not
migraines. IMHO,  that term is really overused. A small amout of caffeine may
also help cure the headache.  A glass of iced tea used to do the trick for
me.
Carol
Your Favorite Dietitian