How to get out of a block ?

How to get out of a block ? Suppose you are stuck on a hard sound , you cant get any sound out, what do you do ? When block happens , my word never comes out no matter how hard i try to. My face is just contorted in fixed position and everything is tense . Any tips ? For example , i decided that im gonna say that word when i approach that person , as i walk towards him/her , i keep on practicing that word in low voice , everything is fluent , but when someone is listening to me saying it , the same word ceases to come out. Sometimes if i manage to say it , situation is made worse , when the person asks me to repeat what i said.