IPhone 4S battery drains overnight?

So i have my iphone 4S and i charge it to 100% before going to sleep and when i wake up in the morning for work before my alarm should have gone on i realise that my phone has gone off and it is out of battery, it has happened twice in the last week and during the day when i check my phone i sometimes have to "Reboot" it by pressing the centre and lock button. Why could this be? Anyone having this problem? Please help!

Added (1). I close all my apps before going to sleep & i turn off my 3G and Wi-Fi connections.

Are you sure you did not live some apps runing on before bed, if is yes then it is not normal. Iphone battery are very very strong to go off like that. Just go and change it, if it possible

It is very easy to know this problem; you must open up a lot of apps, for instance, Facebook, twitter, and digital news apps and other SNS apps, before you go to sleep,

i suggest you to turn off the Wi-Fi and Cellular Data button before you go to sleep

Switch the battery