Mirtazapine
"I've been taking Klonopin for several years, but slowly building up a tolerance.  Doc suggested trying mirtazapine.  Made me very groggy the first night, and I fell asleep quickly.  However, I woke several times during the night, and only ended up getting 3-4 hours of sleep (and felt very groggy the next day).  I might be experiencing some withdrawal from the Klonopin).  Hard to know, but sleep has only gotten worse since the first night, so will likely try something else."