Desperately need to lose weight?!

Hi everyone. :)
I kinda am new to this fasting thing,
and hoping it will help me lose weight.
I am currently 5'3, 167 pounds.
I desperately need to lose weight.
I was not originally this big,
I was actually about 120 pounds...
then I went through a time of deep Depression and gained lots of weight.
Now, I have 8 days to lose some weight.
I was hoping at least 20 pounds...
That sounds really over the top,
but I am desperate.
How would I be able to achieve this?
Exercise + drinking only water?
Also, is sparkling water (seltzer) OK to drink?
Sorry if I sound completely ridiculous,
but this is necessary. :(
Thanks in advance.
xxx