how do you do?

how do you do? How do you do when you really have the words in your head and your practice before speaking, whispering, or softly and the words come out! but when you have to do the real speaking, your mouth just paralyzes and the word is floating in your head like wanting to go out, but you can't move your mouth. That just happens to me every time in online classes. Mostly with words or sentences starting with the "P" letter. it's a hell. Thanks in advance.