normally im having an argument with my cat about how much of the bed he takes up. he always sleeps in some spot that prevents me from getting a good sleep. if i change position, he gets up walks around me 4 times, and then finally settles down in some uncomfortable place. if i close the door he scratches to come inside and meows loudly, id hes in the room he does the same to get out.
other than the cat there are two things which will make it impossible for me to sleep, light, and noise. light is by far the worst. if i can see anything in the room, i just wont be able to fall asleep. noise isnt as bad, and ive been known to fall asleep listening to death metal. but if i hear any kinds of talking or vehicle engines, banging or anything like that sleep is practically impossible.
i also find that if i have a good idea in my head, it will be practically impossible to sleep. fortunately for me, ive done enough drugs in my life where that no longer happens.