I have been on Seroquel for about a year and a half and it STILL makes me very, very sleepy. It is super at block out the racing mind problem at bedtime, but I have to be very strategic at what time I take it or I'll be a zombie the next day. After years and years of not being able to sleep, I don't mind this inconvenience. I have mine set up to where I take the full dose at bedtime. . . I absolutely can't take it during the day.
Hope this helps!