I run into this problem often without touching my Galaxy S5. Just having my phone in my pocket is causing this to occur. Getting to the right menus to turn this off is tedious. But just this moment I accidentally found the cause and an EASY solution. Just triple-click the home button to turn this accessibility mode - vision - talk back mode on or off. Try it... triple-click the home button, and let us know if it solves the problem at least for the moment.