Dear Weelanie,
It is all relative hun. 100kg is actually my first major goal!
However I will say the voices in yuor head will subside after a while. Cravings and the like are your body's way of going
'ere! what's going on!!' as it doesn't like drastic changes. However it gets used to the new regime soon enough and the cravings subside. (Not go away, but get quieter and less frequent. More manageable. Trust me

)
Sometimes you may find that food smells are more delicious, and the colours in adverts are a little brighter, and occasionally you might crave things you havn't eaten in years! (I've been a veggie for nearly 15 years, and it's surprising what suddenly becomes
incredibly attractive) however you just have to realise it's your own biology playing mind games with you, dismiss it, or distract yourself with something. nothing's going to happen to you if you tell your head not to be so daft and go away. (Once you crack that then in a few weeks diet bordom will set in, but that's a different problem entirely...)
5st does seem like an enormous mountain to climb (tell me about it! I was on a real downer yesterday about the 5 st) however if you're dedicated 5 st in 6 months is achievable. If you're really lucky (or in my case, have a monstrous start weight) then 5 st in 5 months might actually be doable.
6 months from now is 16th July. what could you be wearing on 16th July? summer dresses? strappy tops? running the local race for life? Whaever you do with it, 6 months is still going to pass and you don't get it again. Therefore you might as well do something useful with it.
Good luck x