Hallucinations, help!?

I woke up last night and i saw a huge spider about two meters across coming at me from the other side of the room and the whole room was covered in smaller spiders about 2 inches accross. As you do, i started screaming for a minute or 2 until a realised it wasnt real. Can anyone please tell me how i can stop having these hallucinations as ive had other not quite as bad ones before and they realy freak me out. I go to bed farely late bout midnight also it was very hot that night if that makes any difference. Any help will be much appreciated.