Hello, Ann! I'm not quite sure of the context of this sentence. Can you tell me where you heard it? Without a context, this would be my guess:
1. "If you are looked at for more than necessary" could mean that someone is staring at you in a rude or impolite way.
2. "You will look at yourself up and down" sounds a bit odd. Usually, you look someone up and down or someone will look you up and down. You do not look yourself up and down. This phrase also means to stare at someone (also sometimes in a rude or impolite way).
I hope this answer helps! Let me know if you have any other questions.