That is a huge dose. I don't want to sound like a scaremonger but such doses, when used for longer periods (several years), may cause irreversible side effects and damage to your brain. But if you're prescribed such a dose, I guess you're in the need of it. Still, usually only severely schizophrenic people are prescribed such high doses.
If I were you I'd ask the doctor or psychiatrist who prescribed it if such a monster dose really is necessary.
I took quetiapine 4 years for insomnia, 100 mg. Read too much nasty stuff about it and stopped using it. Since then I've used melatonin and/or mirtazapine for sleep.
In the beginning quetiapine makes you extremely tired, lethargic and zombified during daytime but this side effects disappears once your receptors become desensitized. I always got a very stuffy nose from it, sometimes blocking my nose completely. This was due to Seroquel being a powerful antihistamine. Often I had to take nasal spray to get sleep (I have to breath with my nose when I sleep).
I've said it several times but for severe insomnsia, like the OP is taking quetiapine for, try mirtazapine. It's just so much more benign. Its initial sedating effect is IME equally powerful as quetiapine and you don't get much nasty side effects. And, paradoxically, smaller doses of mirtazapine are more sedating than higher (if you don't take monster doses of 60+ mg).