Resting

I'm very tired. I've been up since 12:00am. I want to go to sleep. I've finally finished my work and have just gotten comfortable in my bed; I want to sink into it. I want the dreams to wash over me and seep inside. But I can't; I'm wide awake and feel afraid. I can't go to sleep like this. If I do, I'll have a nightmare that I'm falling down from a great height. It's the same dream every time. All of a sudden, I accidently fall asleep and try to wake myself up but I can't; no matter how hard I try. I'm falling fast, almost on fire. Something's wrong. I scream, but nothing comes out. I hit the ground. I'm still in one piece. Why can't I wake up?