Talk with your friends about this, maybe they can give you some help, otherwise you should consult a psychologist, only thing I can advise you. I'm not a psychologist but I think you lived something that frustratred/scared you in the past, you need to find what is the source of your problem first of all.Then it's just a matter of thoughts, you have to shoo this bad thought and keep concentrating on something else, and for your scary problem, if it can reassure you, buy some alarm, or sleep with your light? I had the same problem once, in Tunisia, at my grandfather's house (in a poor village), my room was in front of a garden where my grandfather grows fruits, and during the night there might be scorpions (because the ground is sand, and scorpions get out of it at night) and I was scaried some nights, I had to check eveywhere before sleeping, under the beds, in the cupboard... I even had to use my torch lamp sometimes to be sure no scorpions were here. That scary thing made me sweating a lot and it took me time to sleep (also, the weather was very hot, my bottle of water wasn't fresh anymore after a moment).