In this short video, Richard Wiseman pinpoints some of the symptoms that are signs of sleep deprivation and even has a small test for you to test your agility. Chances are that if you need an alarm clock to wake up or fall asleep instantly you may need t get more sleep. He has a great resource for those who keep in mind their sleep cycles when going to bed.
Each cycle is about 90 minutes each and to make sure you don’t disrupt a cycle and wake up even more tired. He created a free schedule that tells you when you should go to bed, depending at what hour you want to wake up in the morning.