I've experienced this as well. It's like my sadness drains away into numbness, and except in a few circumstances I simply CAN'T access the negative feelings I know are there. It's like my mind is blocking me off from them, so that I can function.

If I'm talking to my fiance I can cry though, because I feel safe with him. In most other cases it's like I subconsciously feel "nope, gotta cope".

I think it all started with my mother teaching me that me crying or showing negative feelings made HER feel bad and thus I would feel extreme guilt for making her "feel bad" by having feelings.