well...I don't think so, our souls are always active, when we dream, I always think that it is our soul rather than our real body...xxjustsmilexx neds to answer this, shae has more knowledge on the subject:)
as a Musilm I believe that God takes our souls when we sleep and sends it back when we wake up , so while sleeping we are nearly dead that's why when we wake up we say :" praise to Allah who gives us life after he has caused us to die and to him is the the return " and god said in the holy Quran:" Allah takes the souls at the time of their death and the souls of those who haven't died during their sleep . then he holds back those who have died and send the others to a fixed time . Such are the signs for the people who contemplate ." 42 surat. AlZumar
Sorry, had a brain fart there and didn't realize what you were asking. I would think that if there is a spirit, it would most likely enter a "power-saving" state while you sleep. After all, if there is a spirit it's a natural part of the body, and most of our other parts go into standby when we sleep. Or, I think they do anyway, lol.