I can. I can also fake happiness or other emotions that I feel are "allowed". Personally I think I developed that ability through being more afraid and anxious of people finding out about how I felt. At some point it became more of an automatic switch. It's more difficult for me to genuinely react and show what I feel than it is to pretend, which has its own pitfalls. Maybe you aren't super expressive? Or if you show anxiety in atypical ways then people might see without recognizing. There are many possibilities.