Thanks for all the replies..really appreciated. Thanks for the advice about taking it near bedtime and seeing how it affects me - I think I'll do that.
I did mention my concerns to my GP and she said she would be surprised if it affected my sugars (she said the Mirena coil wouldn't but it 100% did, so I'm not sure how much I trust her....). She said I could take the prescription away and think about it before cashing it in...and if I did start it, and didn't like it, I could change to Sertraline or Citalopram... So, I think I might try it and see what happens...I'm just a bit scared of the unknown....