Mindfulness is leading to anxiety and depersonalisation
Simple answer: It's a phase, it will pass.

Detailed answer: Mindfulness meditation doesn't result in a strictly upward curve in terms of clarity or perceived well being. This is one of the reasons for getting guidance from someone experienced, so that they can give you proper feedback on whether you are making progress or not.

If you don't have a teacher/can't find one, I can give you some tools for self diagnosis, let me know in the comments. But be warned, self diagnosis has its own issues and assuming oneself to be in different stage can cause unnecessary and needless suffering that one can do without by just sticking to regular practice.

http://static.squarespace.com/static/5037f52d84ae1e87f694cfda/t/5055922624acbaa64592c1c3/1347785254496/

refer to rows 2 (possible current stage) and 3.1 (possible reason for worsening symptoms)