what makes you go to sleep
It is called circadian rhythms. Humans tend to sleep when it is dark out. I, on the other hand must work all night and sleep in the day. so my natural rhythms are screwed up. Being bored makes us sleepy, reading and watching TV makes me sleepy also physical tiredness.
sleeping is just usual. we already know that we need to sleep. sometimes it is due to tiredness because you can pass a day or two without sleeping. it is a little hard to say what makes us sleep but sometimes you just like to sleep when you're bored.
So, have a warm bath. You will feel relaxed and the sleep will come naturally. You should take a bath with 1 or 2 hours prior to going to sleep, because the steam and that hot water will make you sleepy about 1-2 hours after the bath has been taken.