Maybe it's cold feet?
You've lived your whole life as one gender, following the rules even though it never felt right.
To live as the gender you really are (even if you choose not to go through transition, you can still crossdress to see your true self in the mirror. Thats what I've been doing for now) - this is going to have a huge change on your life and it's scary.
If you really believe this is what you are, don't feel ashamed telling people. It'll be much worse if you suppress it.