Sorry to hear that you're having this problem.

In most cases where an impact hits the screen of an LCD, it breaks the liquid crystals in the panel.

Unfortunately, I'm not sure how to remove a "bruise" from an LCD screen. The panel could be replaced, but typically, that's not an inexpensive endeavor.

Plasma won't "bruise" since it's a glass panel, but I'd consult a retailer in your local (high elevation) area to get their take on how they'll work in your area.