Sleep deprivation is dangerous.
Lack of sleep can cause all sorts of problems; frayed tempers, bad decisions, car accidents. In fact getting your rest is so important that secret moving-about-in-the-shadows types use sleep deprivation as a means to break the bad guys in interrogation situations.
This is true spiritually as well. God designed a system for us whereby we get enough physical and spiritual rest to keep us sane and healthy. The Bible calls it Sabbath rest. God gave us one day out of every week where we should not do any normal work. One day when we focus on Him. This of course doesn't mean that we pay no attention to God the rest of the time, it's just that our Sabbath is a focused, quality day with the Lord.
Britain still, just about, treats Sunday (the day most Christians use as their Sabbath) differently to other days. It tends to be less busy that other days for most people but that's starting to change. There's more to Sabbath rest than just a lie in or leisurely walks in the afternoon. The Sabbath was a gift from God, permission to spend time with Him, to rest in Him. It is a terrible waste not to take advantage of it.
Many Christians too reject the gift of the Sabbath by not taking the time to be in the company of God for more than a couple of hours. We allow distractions to take over, it's a shame. Of course if we get too legalistic over it that can cause problems as well but lets set aside rest time, God and me time.
Proper spiritual rest will aide decision making, calm tempers and produce growth. It is good, it is important, it is a gift - let's not waste it.