We have a lot of knowledge that would be heresy or too bizarre to be useful in the Middle Ages. (You talk about basteria, they'll think you're insane!!) Also, you would be severely lacking in knowledge useful during the time period, unless you are, say, a smith. You'd score big time as a smith, architect, or a skilled artist of any physical product (leathing, clothing, carpentry, etc) Otherwise, you'd be stupid as hell in terms of surviving and everyone would have to teach you how to work and live. You wouldn't have any advantage on the battle field unless you have studied up on the time period to understand the weapons and tactics. You'd be lost in the field of politics.

I don't think you'd do well unless you have a manual skill. However, you would be more equipped in terms of the bubonic plague!!

I am part of a Medieval Reenactment group called the Society for Creative Anachronism. I just came back from a week of camping during a two week event, but I don't pretend that I want to go back in time. I want to stay in the "current middle ages" where we have hot showers and I can run to the grocery store and bring corn for the fire.

My persona is also late 11th century, leaning towards Norman. (1st Crusade time period.)