quetiapine completely knocked me out. i was on the maximum dose, i couldn't think straight, i would stop talking in the middle of sentences, i was barely coherent, i couldn't read which i hated because i love books. it turned me into a zombie and a completely different person, sounds a bit like what you're experiencing. oh, and it had no effect on the mania.
as for mood stabilisers i've tried lithium and valproate, neither of them gave me side effects (that i noticed).
just after xmas i was admitted to hospital after an od, i was immediately taken off quetiapine and despite horrendous withdrawal for the first two weeks i felt a noticeable difference immediately. i am less tired, i can concentrate, i don't feel like my head is made of cotton wool. i cannot believe how i put up with those side effects for 18 months. Are you noticing any positive effects of the quetiapine/carbamazapine? if not i'd say definitely worth thinking about asking if you can try other meds
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