It is a known problem with a few potential short term solutions before a proper fix is found:

http://www.internettablettalk.com/wi...o_sleep_issues.

Note: It is recommended that users Search the site for similar issues before posting new threads, in order to keep discussion orderly for everyone.

Coming up with the right keywords may not always be easy for non-native english-speakers but it is worth the effort and peace of mind.