Why wasn't katniss able to sleep or eat on the night after the fire?

Answer 1

A fireball brushes her calf, scalding her. She manages to put the fire out, but her hands and calf are seriously injured. Eventually the attack ends and Katniss walks until she finds a small pool. The water soothes the burns. She knows she should keep going, but the pain is too great when she takes her leg out of the pool, so she spends the day there recovering. In the afternoon, however, she hears footsteps, and without any alternative she finds a tree and climbs as quickly as possible.It’s the five Careers and Peeta. Katniss calls down to them, knowing they’re too heavy to climb to where she is. Katniss notices that a girl named Glimmer has the bow and arrows from the Cornucopia. A large and dangerous looking boy named Cato begins climbing up after Katniss, but he falls out of the tree. Glimmer goes up next, but she doesn’t get far before she must stop. She fires an arrow at Katniss, but she’s incompetent with the bow and her shot misses. The group decides to wait Katniss out. Unable to go anywhere, Katniss prepares her bed in the tree

Answer 2

Basically it was of her memories of the 74th Hunger Games. Many Victors come out with some kind of scar either physical or mental.