I'm  new to biking and have a ybr 125 custom (2014). Since it came back from having a problem rectified where when I  beaked it fried the fuse - I've been having an intermittent problem where I  have been riding for a while at varying speeds and have to brake to complete stop. As I  try to go down the gears, the gear shift doesn't seem to work and sounds like revs are stuck  even though I'm off the throttle!   
As a newbie it's freaked me out a bit so had to pull to side of road and ler bike stall before I can get gears to drop down and obviously the revs return to normal.   
Any support  would be greatly appreciated.