Turn ofd DND in Silent mode?

[anon(9657076)]

I have been using my M9 in silent mode most days while at work as I find it quick and easy to switch any sounds off. This evening I think I may have caught a button when using my phone as I don't appear to be able to use silent mode without do not disturb being on. If I try to change the profile settings to off for DND in silent mode, it switches my profile automatically back to Normal mode.....can anyone help me??