My phone went through an automatic update yesterday. Now - what a mess! The screen is dim - sometimes it will brighten after 30 seconds to a minute, sometimes not. On dim, I cannot read texts. The personal settings were changed, wallpaper reset, etc. There is a new app (which I did NOT request, and I DO NOT WANT) that I simply cannot delete, etc. Was the update valid, or did I get hacked? (Because if this is an "improvement," then it is an epic fail for the Samsung Galaxy S5.)
It sounds like you got the Lollipop update (legitimate). It has been ... problematic for some (many). Back up all your settings, apps, photos, music, etc using Google or your cloud of choice. Then do a Factory reset; that often will clear up several issues. You wilklhave to redo some settings.
Which update did you get? The initial to Android 5.0 had many glitches, later fixed in 5.0.1. and 5.0.2. Check which version of Android you are running now.