When a block happens, stop, take a deep breath and try again. When I speak with more people, it gets easier over time. So try to face your "fear of tensing up" and interact more with people around you. In the beginning it will be exhausting but it will get better fast. I like to compare it with a bonus system in a game. Every time you "do an interaction" you get points and if you do it more in a short time, your point multiplier rises and you get more points per interaction, if you know what i mean?