Mirtazapine had the exact opposite effect on me. It made me so manic I was hallucinating (bad ones) and didn't sleep for more than an hour for 6 weeks. That was at 15 mg. It did give me terrible nightmares in the beginning but after my manic set on, it turned in to hallucinations. It also made me more aggressive and I even threatened my mom. Got put on an anti-psychotic (abilify) and that wasn't very helpful. But anti-psychotics aren't that bad, they just don't work for everyone. Finally told the doctor to screw it and went off everything and haven't been back.

I am sorry that this is happening to you! Have you been able to contact your pdoc and tell them what is going on? Sometimes it takes about 2 weeks to settle in, but with that severe of side effects I wouldn't be able to wait that long.