After a session of skills practice (escaping the sytem), I was tidying up the back up rope we used, secured to the masterpoint by a lanyard. As I was unclipping the screwgates we used to secure the back up line, I unclipped my lanyard, leaving me unsecured above a 20m drop. I did not realise this until I went to lean back, luckily, before I leant back, I checked where my lanyard was, only to see it dangling by my feet. I swifty made myself safe again.