Could be many reasons for this, best to first discuss with your doc. Also consider using a CBT sleep training program for a comprehensive supportive structure.
morpheus - i don't have an answer but i am struggling with the same thing. my chronic insomnia started up out of the blue and has been going on for 3 months now. i feel so terrified at times because like u i can fall asleep but am jerked awake by the most bizarre sensations in my body and massive terror.
Have you considered talking to your doctor about the insomnia? There are other anxiety meds you can try. Don't stop the medication without first talking to your doctor. Some anxiety meds can have severe symptoms if you stop them too quickly.