Chosen Solution
Want to go back to ios 6
Interface parallax can be turned off in Accessibility settings to reduce the possibility of inducing vertigo. iOS 6 for iPhone 5s does not exist.
Apple has shut down the iOS signing servers for iOS 6. Unless you have a hacked iPhone, it is impossible to revert to iOS 6. However, I agree with @ tomchai. I think the ‘Parallax’ wallpaper feature may be a cause of the vertigo. Go to Settings –> General –> Accessibility –> Reduce Motion, and turn this option to “On”.