Ignore all the advice about resetting the phone, fiddling with various settings, panicking and involving tekko's.
It really is simple. Go to settings. Search "Maintenance Mode", then turn it off.
Your phone will then automatically start and when it refreshes, all your apps have returned. Why? Because maintenance mode needs lots of memory, and turns 90% of your apps off to do its maintenance. Happened to me twice. Both times, fixed in 2 minutes.
That's assuming someone turned maintenance mode on in the first place. It doesnt turn itself on, and you can't do it by accident. Maintenence mode doesnt take energy, it hides apps so they can't be accessed by anyone servicing your phone (or anyone you don't want getting into your stuff if you leave your phone unsecured and unattended)
