2 Answers

Do you know what a "recliner" chair is?  You can, with a push or a button or a lever, cause the back of the chair to lean back, and you can rest and relax in a reclining position.  It is similar to the position in which you find yourself at the dentist's office, only no one has his whole hairy hand down your throat. 

RISE would be to get up, which is not the same as rest, ease, sprawl, or repose. 

You can eliminate many of the words by thinking about them.  REST and EASE are similar, so they are BOTH out, because you are just looking for ONE word.  Repose and sprawl are comfort positions, too though you may need to research their meanings to enlarge your vocabulary.  

ALWAYS look for the OBVIOUS wrong answers first.  

By the way, RISE is the correct answer.  I'm 100% sure of that!