When I was presenting my internship report at the end of university, during some longer pauses somewhere in the middle of it, I just said "sorry, it's little hard". The professors receiving my report responded with warm, understanding smiles. Yeah, and my fellow students chuckled upon it for some time after. But I am glad that I got to say it then, the rest of my presentation passed easier. Of course, you must have courage to say such thing, and for someone it's better to imagine it in advance to prepare, but now I'm surely sure that it is a good way out of it. Probably the best