What is it like having diplopia? can someone describe it?

Double vision: There are multiple types of diplopia due to different causes. Sudden onset of diplopia which does not resolve needs immediate attention. Also recurrent diplopia needs medical attention. Other forms can be transient and short lived due to use of certain medications.

Two images: You can easily see what it is like if your eyes are normally signted. Simply press on the eye through the lid which will displace one image and you will see two images. That is what it is like. Someone who has it cannot tell which image is real and which is displaced which is why they will close one eye to prevent the doubling.