I was on Seroquel a couple years ago for sleep, but a pretty good dose (200 mg I think), and I was able to titrate off of it and onto something else within a week. I didn't really have any issues. That's probably not very helpful. I don't know what you're taking the lithium for, but they work pretty differently and for different things. Do you know why your doc changed you to lithium from Seroquel?