I usually go blank before I can even start talking, strangers find it odd. Sometimes in a shop people first ask me a question in finnish, then in swedish or english. And I just stare. It's embarrassing!
My mom has patience with me when I go blank in the middle of my talking. She just stands there, says ''Go on'' or ''You can tell'', and waits. She's so lovely <3

I think it's about not being able to focus which can be caused by things like stress and tiredness.... But I think you can always say (and many people do) ''I forgot what I was saying.'' Many people will wait when you gather your thoughts or they will tell you what you just said and it can help. It helps my cousin every time.