I have a friend called Kaissie we've been friends for about 12 or13 years, and I have feelings for her, but I am afraid that she might say no, because we've been friends for so long. Am I in a friendzone or am I just hallucinating..

There is no way for us to know. You would know better than anyone here.

Why not try asking her out?

How old are you and what makes you think you are hallucinating? Has she given you any indication she may like you are anything other than a friend?
What kind of feelings do you have for her? Is this hormones or do you generally like her. Sometimes when you've known someone for so long as you get older you think there should be something there.

12 -13 years wow, must be very good friends. How old are you? Just ask her like good friend to have a coffee and watch movies together. Keep it slow. Bring her flowers and chocolates. Drive her home. And see how she takes these gesture and slowly in week or two ask her for date. There nothing wrong being in friendzone.

You are 16 of course you have feelings for this childhood friend. To bad you are so scared of rejection to even ask her out. To bad you are so confused about your own feelings to enjoy the friendship.

Enjoy the friendship and see where it goes. Don't get wrapped up in the dating thing.