Viewport flips upside down?

I got a strange one. I have a level that has several sublevels in it. At some point the level has decided the camera needs to be flipped in the Editor. The render is inverted, such that (for example) panning the camera down appears to move it up etc.

In-game it works fine, just in the editor it’s upside down.

I can’t pinpoint the exact time that it started happening, but since I’m able to work through it I haven’t tried to fix it.

Interaction is fine, clicking on objects works as expected etc. Just really strange.

Any ideas?

Nevermind, found the answer in
Resolution is to hold alt then left-drag. Why is that not really mentioned anywhere? And why does it lock upside down? Weird…