my third eye has always been the most open. having a chakra too open can be a bad thing just as having one closed is. if it's black you'll suffer from headaches, too open and your imagination can run wild. a balanced third eye you can have psychic prediction and clairvoyance. you won't have many headaches and you're imagination won't run wild. as a child i had an overactive imagination. mine was as a kid and still is, just means i do a lot of art and writing so i keep focused on reality. boring dull reality.
i don't know what i feels like to open it, because as i said, but when i open the others, i've felt different. the root, i didn't feel at nervous. you will be able to hear/see spirits better too when you open your third eye. just be sure to work on all of them, because it's not good to work with only one.