Are you talking about
anxiety from w/drawal? A low dose of Seroquil will help, or some
Clonidine, not Klonopin. Both are very sedating. Those are the only two that worked for w/drawal insomnia for me.
If it's caused from an actual anxiety disorder, there are quite a few meds out there, but all work differently for different people. I take Xanax for horrible anxiety, (GAD, social phobia and panic disorder). 2mg's before bed will slow down my thinking but not put me to sleep.