Does anybody know much about LITHIUM CARBONATE?

My doc has today put me on Lithium Carbonate 250mg at night as I havent been able to get to sleep at night properly for ages or at least at reasonable times. Before medication I didnt have a problem getting to sleep at all all my life! She is also using Lithium Carbonate to "augment" (go with) the very low dose (20mg) of fluoxetine i am on for depression and anxiety, as when she increased my dose of fluoxetine it only increased terrible feelings of depression/feeling suicidal, it actually made me feel worse! I have tried to do some research on Lithium this evening, but i can only find info on it for treating bipolar really. I dont have that - just GAD (Generalized Anxiety Disorder & Depression). Yes apparently it can be toxic and kill too (why do all these meds have to be so damn scary!?!) so she will send me for regular blood tests too just to ensure toxicity does not occur....Can anyone enlighten me? Anybody been out there and had good results for treatment resistant depression? Or sensitive to medication? Does it truly help elevate mood???