Read the following context and choose the best option to answer the question.
Context: When he removed it , he found that he was alone . With some difficulty , he managed to sit up and grabbed the waterskin from his bag , drinking his fill . Something was wrong . He did n't normally sleep this much , even given the opportunity . He usually did n't require much sleep .
Question: What is causing the anxiety of the subject ?
Options: 
- They are low on water .
 - They are getting too many z 's .
 - They are   low on drink .
 - None of the above choices .


They are getting too many z 's .