It's worth mentioning that God Himself ordained a day of rest for Himself, and His people (yes, we know God doesn't get tired!), and that rest is one of the gifts of the Creation.
Many things happen during our sleep times, and the physiologists are just now discovering the importance of sleep (for a summary of this from a natural health perspective, see the following links:
Dr. Mercola's Articles on Sleep (you may have to register on the site to read the articles, so be warned).
GreenMedInfo on sleep
Modern research places sleep as one of the great health and immune system strengtheners, and it's been known for decades that insomnia shortens life.
However, sleep also has a component that for me is particularly helpful. When I am in fellowship with God, I think when I sleep. I actually produce as I sleep, and many times my subconscious (??) solves problems and strengthens me spiritually as I rest. I also find that I pray better when I rest properly, and many of my real breakthroughs with the Lord come when I am in that "space between waking and sleeping," where my intellect is not impacted by all sorts of outside influences. In other words, rest has been very important to my spiritual life. It enhances my meditation, and fills me with a deeper understanding of the Lord, and of my spiritual life.
So when David says,
Psalm 4:4 Stand in awe, and sin not: commune with your own heart upon your bed, and be still.
and
4:8 I will both lay me down in peace, and sleep: for you alone, O LORD, make me dwell in safety.
It means a lot more to me than just "going to sleep;" it's a spiritual exercise that refreshes, strengthens, and prepares me.
Sleep is a wonderful gift, as is rest. For those of us who are partial insomniacs (I've been there), it's a precious and infrequent blessing, like water in a desert land.
You can develop a spiritual approach to sleep, in which your life with God is extended and strengthened even to your periods of rest (see the first verse I quoted for a hint of this). I'll talk about that later.
