since about the age of 15 i have never been able to sleep properly. i get like 4-5 hours on a good night. since its been such a long time though i am use to it and feel no real side effects ie i am able to concentrate etc. its just one of those things if i lie in bed after that time nothing happens so i just read a book, watch tv or internet. even if i did alot of streneous exercise ie sex still 4 hours later i am up. thats when its a bitch when you have someone next to you or with their arm around you sleeping whilst i can't move and are therefore reduced to staring at the ceiling for the next 5-6 hours 
