Hp prime erased all my data

[slysalamander]

Hello
I bought an hp prime a month ago.
Today I took it from backpack to use and it didnt turn on. Last time i used were 3 days ago.
I arrived home and plugged it to charge.
The battery probably reached 0.
But now all my programs are gone. All my data was deleted, programs and all my user variables.
I had a lot of notes that were important, and i wonder if there is a way to recover.
I didnt had any backups.
The weird part is that the clock is still right, and the black wallpaper is still black. So i think it didnt factory reseted. What could have happened? It is so weird that everything is gone.

What did i do wrong?
If i do backups i can prevent this from happening?
How can I recover my notes and programs?
Should I leave the screen on when it's charging?

Hope someone can help ?
Thanks in advance