I'll help you figure this out. What version of Photoshop & the operating system are you working on? Does this continue to happen after you've restarted Photoshop & the computer?
Your description matches what happens when we hold down the ALT/OPT key on the keyboard.
Try pressing the ALT key on your keyboard to check whether it is stuck. You can also use the On Screen Keyboard to check what key inputs are active.