Sensing darkness / getting chills / suddenly feeling terrified after looking making eye contact with what seemed like a friendly old lady?

This is the second time in my life I have encountered this feeling. I know I sound crazy but I'm not. I was doing a makeover my a client and she was a friendly old lady, but as soon as we made eye contact my stomach dropped and I sensed a chilling presence near me. I was honestly terrified and couldn't look her in the eye.. But carried on a friendly conversation. This happened a few years ago once too. I am not religious. But her presence terrified me. Please suggest what it may have been... Her eyes were somewhat hypnotising