Seroquel at lower doses mainly binds to histamine receptors, which is why it gets used off label as a sleep aid at
low doses. Sleepiness *might* be from lowering your seroquel
dose to 75 mg from 300 mg. While seroquel is known for being one of the best atypicals for the depression phase of bipolar, many atypicals are mood stabilizing and cover both mania and depression.
One thing you might ask your doctor if you can try is stopping the seroquel and starting abilify in its place.