This happened to me today while I was trying to use my iPhone 8. I was using Outlook for iOS (I know the image below is different but it was hard to take a screenshot at the time), and anyways, I wondered how the heck does that happen?, why is everything upside down?. Well, there is a fix for this.
Simply put your finger at the bottom of the screen and slide upwards, and then you will see a control panel. Then, when you see the control panel, simply click on the icon that has an arrow going around in a circle, and then your apps should no longer be upside down after that.g