It's definitely a sign that your hormone balance is changing. I know at the end of pregnancy, your body goes from having a progesterone to an estrogen dominance. The night sweats thing is something many women do not experience until after the baby but I know that
a) weight loss or lack of gain
b) swelling going down
c) night sweats
are all part of that water loss at the end of pregnancy. Unfortunately, I do not know how long between this and before labour actually starts.
Other signs (just for fun)
a) increased BHs, stronger, longer, at times regular
b) bloody show
c) mucus plug - could be clear, bloody, pink, dark, thick and plug like, thin stringy bits.
d) dramatic change or increase in cervical mucus (may be because of the hormonal changes or be the mucus plug
e) baby dropping, lightening, engagement, measurement smaller, less heartburn, easier to breath etc... (all related)
f) irritable mood, elated mood, nesting instinct, sleepness, renewed energy
These are some of my favourite things!!
Anyhow, there seems to be women who have one or more of these symptoms and go into labour within hours and others that have all of them and don't go into labour for weeks.
Dilation and Effacement is the same. Generally 4cm and thin means labour is imminent but not always... Darn it all!
Good luck to everyone!