Hey!
I had this problem with all relationships that I was before. Mostly because I don't trust people my emotions.
This changed last summer, when I met the girl of my dreams and from first sight I decided that I will be completely, bluntly honest with her.
No matter what she asked, I always said truth, no matter how awkward this was to me. My reasoning behind it was that if we get together, I want her to like real me, with all my personality and mood swings.
This helped big time. We bonded super fast. I give this advice to everyone.
You have been with her for 11 years. Is there something she will not like You for?
If You are tired, say so, tell her You got a lot on Your mind lately. If she asks what. Answer. If You are not sure, say so, but try to give some logic into it.
For example: I'm not sure, but it could be that I'm bit stressed out at work. Or I want to do something new, would You want to go to small trip with me over weekends.
Why this helps in my opinion? Because You will be honest to Yourself, as well.
Good luck!
Best regards,
W.A.M.