English learners very often don’t remember the words they want to say. That’s when this phrase comes in handy:

my mind goes blank / is a blank

If your mind goes blank (also is a blank) , you suddenly cannot remember something: 

I tried to remember her name, but my mind went completely blank / was a complete blank.

For some reason, her mind went completely blank / was a blank.

I went blank and couldn’t think of a single example.

When she asked me his name, my mind went blank.

blank verb (FORGET)

To forget something that you know:

When he tried to remember the lyrics, he blanked.

I completely blanked on his name.

Now, if you have already learned well the phrase my mind goes blank, what about learning another one that will tell you what you have to do when your mind goes blank? Listen carefully and take notes.

https://dictionary.cambridge.org/pt/dicionario/ingles/go-blank

https://dictionary.cambridge.org/pt/dicionario/ingles/blank

https://dictionary.cambridge.org/us/dictionary/english/your-mind-is-a-blank-goes-blank