Yep, I have this problem, too. I find that there are two types of situations with which I struggle:

1. Times when I'm afraid to say no to a request or something else innocuous. This is when I end up taking on more responsibilities at work or doing things for friends that don't really want to do. I'm getting better at saying no in these situations as I grow more confident and assertive in looking out for my needs.

2. Times that are more threatening in which I am too scared to speak, even to say no. These situations tend to be more physical, like when I am in public and someone gets too close or a stranger makes a request. It also includes situations where trauma stuff gets triggered for me and I feel more "then" than "now." This is harder to cope with.