Seroquel is one of the 'atypical antipsychotics' that came out about ten years ago. They were first used for serious mental illness like schizophrenia, and then for bipolar disorder, and then for the thing we 'call' bipolar in children, that really isn't bipolar disorder. Seroquel is one of the most sedating of the group (zyprexa is quite sedating as well) and so it has been used as a 'non addictive sleep medication' in very low doses-- although many institutions are trying now to ban it for that purpose for cost concerns.
When Seroquel is used for bipolar disorder, it is used at up to 800 mg per day; for sleep it will be used at 25, 50, or 100 mg. The main side effects to Seroquel are weight gain and 'metabolic syndrome', which consists of a group of conditions that make diabetes and heart disease more likely. The studies showing these effects were using doses higher that 'sleep doses', and the risks from low doses are not really known.
I doubt that it did something 'permanent' to your ability to sleep; any sedating medication will cause some insomnia when it is first discontinued-- for a few days at least. When I stopped opiates it took a couple months before I started sleeping well again.
Thank you Dr. Junig for your response, it is much appreciated!