What is the best course of action to follow should you lose your train of thought during your speech?

Personally, I would address the problem, explaining to your audience that you've lost your "train of thought" from there, make fun of the situation, say "let's see, where was I?" * recieve an answer from audience * then continue one.

To sum it, make fun, and a light hearted joke about it, and continue to your best ability.

Understanding to your people that you've lost your train of thought from there, make fun of the situation, say let's see, where was I in a funny manner