How does Gregor initially react to his situation?

After examining his new physiology, complete with numerous thin legs, a hard back, and a segmented belly, he wonders only momentarily what has happened to him. His attention is quickly distracted as he observes his room, noting its small size and seeing on the wall a picture of a woman he had clipped out of a magazine and framed. Wanting to go back to sleep, Gregor realizes that he cannot turn over on his side, which is the only position he can sleep in