Fortnite PS4 controller button issues
There is probably a setting to invert the Y-axis in the options menu. I do not have Fortnite, so I cannot check it, but many other games do have it. Toggle this setting, and it should be normal again.
It is on inverted axis. You can change this in the "controls" settings. Once done, it should be fine. I had to fix this when I played, too.