Searing heat is blanketing much of the U.S., putting millions in danger. The majority of the country will see temperatures above 90 degrees, with heat indexes soaring to 110 degrees along the East Coast. So what are the signs of heat stroke that you should know? Inside Edition asked Dr. Mehmet Oz for tips to recognize the illness. Oz advises staying out of the sun altogether this weekend. But if you must go out, make sure to drink lots of water, at least half a gallon a day.